CIS 442 Computer security

Chapter 7

Network security

7.1. Internet Vulnerabilities

A network vulnerability is an inherent weakness in the design,

implementation, or use of a hardware component or a software routine.

A vulnerability invites attacks and makes the network susceptible to threats.

A threat is anything that can disrupt the operation of the network. A threat can

even be accidental or an act of nature, but threats are mostly intentional.

A threat can damage the network, slow it down, or make it unavailable. Any

type of rogue software represents a threat.

An attack is a specific approach employed to exploit a known vulnerability.

A passive attack is designed to monitor and record network activity in an

attempt to collect information to be used later in an active attack

Examples of passive attacks are packet sniffing (page 226) and traffic

analysis.

Passive attacks are difficult to detect.

7.2. Port Scanning

When two programs on different computers exchange data, all the data

packets sent between the programs have (among other specifications) the

same port No.

Accessing a network opens a port and is similar to opening a door. This

makes ports especially important for network security.

When data packets arrive at a computer from different sources, each stream

of packets uses a port number. A port is identified by a 16-bit integer and

there can be up to 216 − 1 = 65,535 ports.

There are three classes of ports, well known (0 through 1023), registered

(1024 through 49,151), and dynamic/private (49,152 through 65,535).

The well-known ports are assigned by [IANA port 04] and are normally used

by operating system processes. Some examples are FTP (port 21), TELNET

(port 23), SMTP (port 25), and HTTP (port 80).

Registered ports are typically used by user applications (as opposed to

operating system processes) when they have to contact a server, but such

ports can also identify named services that have been registered by a third

party.

Dynamic/private ports are used by user applications, but their use is rare.

Such ports do not have any meaning outside of any particular TCP

connection.

A port scanner is a program that listens to data arriving at and departing from

certain ports on a computer.

Port scanning has legitimate uses in managing networks, but is also used

heavily by hackers to gather information that identifies open doors to the

computer.

Information collected by port scanners is used to identify operating system

utilities installed in the computer, and exploit known vulnerabilities in those

utilities in order to break into the computer.

Port scanners are implemented by sophisticated hackers who make them

available on the Internet.

There are several types of port scanners as follows:

Vanilla: The scanner attempts to connect to all I/O ports.

Strobe: A specialized scan looking only for certain services to exploit.

Fragmented packets: The scanner sends fragments of packets. Such

fragments can sometimes get through certain packet filters in a firewall.

UDP: The scanner looks for open UDP ports.

Sweep: The scanner connects to the same port on several (even many)

computers.

FTP bounce: The scanner goes through an FTP server (to appear legitimate).

Stealth scan: The scanner partly disables the log service of the operating

system, so it (the operating system) can no longer record the scanner’s

activities.

Web site [dslreports 04] offers a free service looking for port scanners.

Nmap (Network Mapper) from [insecure 04] is a free open source utility for

network exploration and security auditing. Among other checks, it looks for

port scanners.

Spoofs

The term spoof means to pretend to be someone else, to falsify one’s identity,

or to cover tracks. It is no wonder that various spoofing methods are used by

hackers to gain access or to obtain information.

This section describes various techniques for spoofing over a network.

IP spoofing. A computer may be protected from attack by restricting the IP

addresses that may send it data. A router may have a list of IP numbers and it

allows only data from these numbers to enter the computer.

A hacker who has this list may spoof the router by sending data that appears

to have come from a legitimate IP address. Someone who doesn’t have the

list may discover an allowed IP number by sending the computer data packets

with consecutive IP numbers until a packet gains entry to the computer.

Defending against spoofing is never perfect, because it involves built-in

weaknesses in the TCP protocol. However, a full understanding of the

problem, combined with a few simple precautions, can reduce this threat.

The defense involves two main techniques as follows:

Filtering. If the computer is part of a local area network, the network has a

range of IP addresses. When data is sent outside a local network (uploading),

the filter software at the router should block any source IP outside the range

of the local network.

This prevents someone in the local network from sending spoofed data

outside the local network.

When data is received (download), the filter should block any packets with

source IPs that are within the range of the local network.

Encryption and Authentication. There are Internet protocols that specify

the details of data encryption and how to authenticate messages.

While imperfect, such protocols may help to eliminate simple IP spoofing

attacks.

Sequence number spoofing

The TCP protocol specifies the use of sequence numbers within data packets.

Each data byte has a sequence number, and the receiver must acknowledge

the sequence number of the last contiguous byte it has received.

When TCP connection between two computers (server and client) is

established, the server selects an initial sequence number (ISN) and

communicates it to the client by means of the three-step protocol.

The ISN becomes the sequence number of the first byte of the first packet.

If the packet contains N data bytes, then the last byte has sequence number

ISN+N−1. Thus, the first data byte of the next packet has sequence number

ISN + N and this number is included by the server in the packet’s TCP

header. For each packet received, the client sends an acknowledge where,

among other items of information, it indicates the sequence number of the

last contiguous byte it has received.

This tells the server how much of the data has been received by the client as

one contiguous block.

Session hijacking

This type of attack occurs when a hacker gains privileged access to a network

device, such as a router, that serves as a gateway between the server and

client.

The hacker can, in such a case, use

IP spoofing to take over the entire session of data transmission and send any

information, rogue programs, and corrupt data to the client’s computer.

Most authentication in the TCP/IP protocol takes place at the time the

connection is established, and this can be exploited by a hacker to gain access

to a machine by, for example, using source-routed IP packets.

This allows a hacker at node A on the network to participate in a data

exchange between B and C by placing himself in the middle and routing the

IP packets to pass through his machine.

DNS

A domain name server (DNS) is a computer used specifically for networking.

It has a dictionary with IP addresses and the corresponding URLs.

When a computer wants to send data, it has to prepare packets with the IP

address of the receiving computer.

The human user normally knows the URL (a meaningful string), so the

sending application has to connect to the DNS first, send it the URL, and

receive the corresponding IP address.

Only then can the application send data with the proper IP and TCP headers.

This is why, when we want to browse a certain URL, the browser often

displays the message ―looking for. . . ” for a few seconds.

One threat related to DNS is man in the middle (MIM). A hacker may register

a domain name, such as aple.com, that is similar to an existing popular URL.

When a user mistypes aple instead of apple, the browser receives from the

DNS computer the IP address of the hacker’s site, and connects to that site.

Now the hacker is in control. His site can display information similar to that

displayed by the real site, while also sending its own malicious software.

The hacker can even retrieve from apple.com the web pages the user wants,

then forward them, perhaps modified, to the user.

Another option is for the hacker to insert himself ―inline‖ between a user and

a Web site using a sniffing program to intercept the exchange of data between

them.

DNS poisoning

Another threat related to DNS is DNS poisoning. In the past, the most

common DNS software was the Berkeley Internet name daemon (BIND).

Early versions of this software had weaknesses that made it easy for a hacker

to modify the IP addresses associated with any URLs.

Once a hacker changes the IP associated with, say apple.com. Anyone trying

to connect to that URL will be connected to the hacker’s site, with potentially

disastrous results.

A well-known example of DNS poisoning is the defacing, in 2001, of the

Web site of RSA Security [RSAsecurity 04].

The anonymous hijacker rerouted visitors from RSAsecurity.com to a fake

site that looked like the RSA site but was different in significant ways. \

Anyone who noticed the differences in the Web site, assumed that RSA

Security, an important developer of encryption techniques and products, had

been compromised. In fact, only the DNS was attacked and corrupted.

Spam

• Spam is unwanted, unsolicited email sent in bulk to many unwilling recipients.

• Most of it is commercial advertising for dubious products, get-rich-quick

schemes, or quasi-legal or health services.

• In April 2009, Microsoft’s biannual report on the state of computer security

estimated that 97.3% of email traffic was unwanted spam (or malicious email

like phishing attacks and outright viruses).

• Surprisingly this was down a bit from the first half of 2008, when total spam

volume reached a whopping 98.4% of all email sent.

• Also in April 2009, Google estimated that about 94% of all email traffic

monitored by its Postini services in 2009 represents spam.

• A central computer dedicated to sending and receiving email for a large

organization can be attacked by sending its many users massive quantities of

identical email messages.

• This consumes valuable network bandwidth, it overloads the CPU, eats up disk

space on the email server, and can cause it to crash (by overflowing some data

structure) or freeze (by keeping the CPU permanently occupied with receiving,

logging, sending, and forwarding the spam messages).

• URLs such as Specialham.com and Spamforum.biz (both now defunct), which

are hosted mostly in Russia and China (but also in Florida), may not look very

useful or interesting to a casual visitor or even to security-conscious persons

such as readers of this book, but are familiar and very useful to spammers.

• These sites also carry advertisements for bullet-proof hosting (ISPs, most of

them Chinese, that allow spam) and allow spammers to exchange news and

information.

• The news is mostly about steps taken by ISPs and law makers and enforcers in

various countries to make the lives of spammers more difficult.

• Much information is offered on ISPs and networks that close their eyes to spam

in return for the high revenues obtained from spammers.

Spamhaus maintains a register of known spam operations (ROKSO) database with

names, addresses, and much information on the top 200 spammers. In early June

2005, the top ten were the following:

• Alan Ralsky. Operating mostly in Michigan, United States. One of his

companies is Additional Benefits, LLC. Michael Lindsay. Mostly in California,

United States. Companies are iMedia Networks, InterNetco Communications,

and GalaxyNET Telecom.

• Andrew Westmoreland with partner Kai Bannon. In Florida and Texas,

United States. Operate under Internet Access Group, Inc.

• Jeffrey A. Peters, CEO of JTel.net (or CPU Solutions) Corp. Located in St

Petersburg, Florida. Mr. Peters disappeared from the spamming business long

enough for his spamhous ROKSO records to expire during 2004, but has

reappeared in early 2005.

• Alexey Panov. Claims to live in Russia. Company is Trendlogic GMBH

located in Germany. Email ckync@ckync.com.

• Ivo Ottavio Reali Camargo. Operating from his office in Florianopolis, Santa

Carina, Brazil.

• Ruslan Ibragimov. Moscow, Russia. Web address send-safe.com.

The four main reasons why spam is so bad are as follows:

1. It is easy to send. All that a spammer needs is spam software and a fast

Internet connection Such a connection may send a flood of millions of

identical messages a day, while costing only about $100 a day.

2. Many spam messages ask the user to click on a link to be removed from

the mailing list. As many of us have found, clicking to be removed from such

a list at best verifies to the spammer that the email address exists and at worst

may result in a virus infection.

3. Spammers tend to use computing resources illegally or even to steal them

outright. A spammer may employ an Internet attack to get hold of a PC, then

use that PC to forward its spam messages

4. Spam is trash. We have all seen messages advertising worthless merchandis

and deceptive or fraudulent services.

• One scam to avoid is contests. Contests are very often used as bait to lure

unsuspecting users to submit their names, physical addresses, telephone

numbers, and email addresses.

• Your chance of winning in a real contest are so small, and the number of fake

contests is so large, that it’s not worth it to participate in them. The same is true

for sites offering prizes.

• The best policy is to ignore contests and prizes.

• Another important technique of collecting email addresses is harvesting them

(some prefer the term scavenging) from the Who is data base at [Network

solutions 04].

• Internet search engines are common and very useful. Such an engine works by

crawling the Internet, locating Web pages, and saving and indexing them.

• Along the same lines, spammers use spambots, software that crawls the Web,

examining Web pages looking for email addresses, and harvesting them for

future abuse or for sale.

• An obvious (but alas, not ideal) protection is to obfuscate all email addresses in

a Web page. Instead of writing an email address in your Web site in a form

such as leopold.bloom@ulysses.name, it is better to have something like

leopold bloom at ulysses dot name.

• There are commercial services that provide relief from spam for their members

by blocking it.

• A typical spam-relief service maintains a list of approved senders and asks each

of its members to provide their own list of approved senders. The service ―sits‖

between the member and the member’s mail server, and the member uses the

same email software to send and receive messages.

• A simple technique to reduce spam is to open several alternate email address.

When one gets flooded with spam, tell your correspondents to use another one.

• There are several large companies, such as Yahoo and Hotmail, that provide

free email addresses, but they are frequently targets of massive spam and

various attacks.

• A common sense idea is to avoid giving out your email address as much as

possible.

• If you have a Web site with your address, try to write it in the form john at abc

dot com or a similar format.

• If you set up a message board or a discussion group, try to display just part of

any email address.

Zombies.

Certain types of malware are used to capture control of a computer and

command it remotely. Such a captured machine is known as a zombie and a set

of zombies is termed a botnet.

• A botnet is an ideal means of hiding the identity of a perpetrator and security

experts see more and bigger botnets all the time. It is known that DoS attacks

are often carried out after the attacker has gained control of many computers

and turned them into zombies.

• A targeted Web site is flooded with a vast number of meaningless messages

sent by computers whose innocent users know nothing about the attack. The

attack keeps legitimate users from using the site, causing inconvenience to

users and monetary losses to the site’s owners.

• Such an attack is referred to as distributed denial of service (DDoS).

• Zombies are also used by spammers to hide their identities. A spammer who

controls a zombie computer, sends this slave a (normally stolen) list of email

addresses and instructs it to send a message (or several messages) hawking

useless merchandise, fraudulent schemes, or unwanted services to all the

addresses. Zombies are less destructive than viruses or other types of rogue

software because they rarely damage data.

• Even if you don’t reply to spam, there are ways for the spammer to verify that

you have received and opened it. Some examples are:

• If you have your email program set to preview messages (i.e., to show you the

contents of the message in a window below the list of email), the spammer may

be able to verify that the email has been received.

• If you click on a link to unsubscribe from a mailing list, you have confirmed to

the spammer that your email address is active. The spammer can then sell your

address to others.

• Spammers can include a ―web bug‖ in an email. This is a link that connects to

the spammer’s Web site as soon as the email is read o previewed.

• If you want to avoid letting spammers know that their mail go through, follow

the advice given here.

How to avoid spam

• Use anti-spam software, update and run it regularly. This software can

significantly reduce unwanted email, especially if it is programmed to receive

feedback from the user/reader and employ it to learn (from the subject line or

sender’s address) which messages are spam.

• Never buy anything advertised by unsolicited email because this only

encourages future spam.

• Once your email address becomes known to the seller, it will be added to the

huge address lists that are sold to other spammers, with the result that you’ll

receive even more junk email.

• Worse still, responding to spam advertises you as a sucker and opens you to

further fraud and identity theft attempts.

• If the sender’s name sounds unfamiliar, delete the email without any hesitation.

Most spam is just a nuisance, but often it includes viruses and other nasty

software.

• Never respond to spam messages or click on any links in them. Replying to

spam—even to unsubscribe from it—confirms to the spammer that your email

address is a valid one, thereby encouraging more spam.

• Opt out of any further information or free or attractive offers. When you fill out

forms on the Web, uncheck any checkboxes that offer further information or

offers.

• Don’t use the preview mode in your email viewer. Spammers can verify that a

message has been previewed, even if it hasn’t been opened because the preview

effectively opens the email.) Knowing that you have read their messages

encourages the spammers.

• Try to decide whether an email message is spam based only on the subject line

and sender’s name and address. Use the bcc field if you email many people at

once. The bcc (blind carbon copy) field hides the list of recipients from any

individual recipient. If you include the addresses in the To field, spammers may

harvest them and add them to mailing lists.

• Restrict the use of your email address on the Internet. Don’t publish it on Web

sites, newsgroup lists or other online public forums.

• Spammers have software that crawls the internet to find addresses in such

places, harvest them, and add them to mailing lists.

• Give your main address only to those you trust (and even then be ready for

your address to be discovered and abused by spammers).

• Always have several secondary email addresses ready. (Those are easy to open

at sites such as Yahoo, Gmail, and emailaddresses.com) When you fill out Web

registration forms or surveys on sites with which you don’t want further

contact, use a secondary email address.

• If the secondary address is flooded by spam, simply close it. This protects your

main address from spam.

Denial of Service

• Many Internet attacks try to obtain private data or to damage data. In contrast, a

denial-of-service attack aims to shut down an entire network, a single server, or

a particular Web site.

• The attack tries to prevent legitimate users of a service from using that service.

• This can be done by one of the following methods:

• Flood a network with traffic. This makes it hard or impossible for legitimate

users to send or receive data.

• Disrupt connections between two computers. This prevents remote access to

the machines.

• Attempt to prevent a particular user from accessing a service.

• Disrupt or prevent network access to a particular computer or network.

• A hacker may open an account at an ftp site, then store data and retrieve it

repeatedly, thereby consuming disk space and monopolizing network services

at the site.

There are three types of denial-of-service

1. consumption of scarce or nonrenewable resources,

2. destruction or alteration of network information, and

3. physical destruction or alteration of network components.

• The first type, consumption of scarce resources, relies on the fact that

computers and networks need resources such as electrical power, CPU time,

memory space, disk space, and network connections.

• The easiest resource for a hacker to consume is network connectivity. It is

possible to tie up the network connections of a computer, such that it waits for

some data that never arrives, so it remains hung up. All that the hacker has to do

is start opening a connection to a network server but never complete this process.

• The victim server has reserved a port and a data structure for the connection,

but the port remains half open.

• The hacker (or a group of coordinated attackers) can very quickly tie up all the

available ports of a server. In the meantime, other users, legitimate or not, who try

to establish connections are denied access. Such an attack is called a SYN flood.

• Even someone with only a slow computer and slow modem can stop a large

server very quickly. Here is a detailed description of this threat.

• A typical client/server network consists of a server (a computer with files that

are useful to a group of users) and many clients (users who want access to

those files).

• When a client tries to connect to the server, both the client and the server have

to execute a connection protocol.

• They have to exchange certain messages that establish the connection. This is

true for all the TCP connections, such as email, telnet, and http.

• In its simplest form, the protocol starts when the client sends a SYN message

to the server. If the server is ready to open a connection, it sends back a SYN-

ACK message, expecting to receive an ACK message from the client. When

this is done, communication can start.

• Echo (defined in [RFC-862 04]) uses UDP and TCP port 7 and is employed as

a debugging tool. It sends any data packets received from a source back to that

source.

• An infiltrator can create a DoS attack by spoofing an IP address and causing

two computers to send packets with random data to each other.

• In more detail, by connecting a host’s chargen service to the echo service on

the same or on a different computer, all affected computers may be effectively

choked because of the huge number of packets produced and sent.

• In addition, if several computers are connected in this way, the network

connecting them may also become congested and deny service to any other

computers whose network traffic needs to be forwarded by that network.

• An attacker may also generate a huge number of data packets and send them to

a target computer. This is a bandwidth consumption attack that may involve a

group of intruders.

• An attacker may also consume massive amounts of disk space by, for example,

generating many email messages, generating errors that have to be logged, and

reading huge files from anonymous ftp servers and writing them on the disk.

• When the disk is full, this attack stops, but when the user needs more disk

space later, the operating system issues an error message (disk full).

• An intruder may be able to cause an operating system to crash or to become

unstable by sending unexpected data over the network.

• A well-known example of such an attack is called the ping of death.

• Hackers have discovered that such an attack is particularly ―successful‖ when

the large data packets are sent as part of the Internet control message protocol

(ICMP). ICMP is a component of the TCP/IP protocol that transmits error and

control messages between computers.

• Two specific data packets specified by ICMP are ECHO_REQUEST and

ECHO_RESPONSE. These are commonly sent by a computer to determine

whether a remote computer is reachable via th network and are commonly

known as ―ping,‖ which gave this particular attack its name (the name ―smurf

attack‖ is also sometimes used).

• The original ping program was written as part of UNIX by Mike Muuss and

generated so much interest that the ping concept became part of the Internet

protocol.

• If your operating system is experiencing frequent crashes with no apparent

cause, it could be the result of this type of attack.

• The obvious defense against the ping of death is to patch the low-level routine

that sends data packets to never send large packets, and patch the routine that

receives packets to ignore packets that are too large. In practice, this should be

done by the makers of the operating system and issued as a security patch.

• The second type of DoS threat involves destruction or alteration of network

information.

• An attacker may be able to change the IP number of a victim’s personal

computer, change the registration of the operating system, or change

prerecorded telephone numbers used by the modem to call outside servers.

• The third type of DoS threat involves physical destruction or alteration of

network components.

• This can be done by an intruder physically appearing in a computer center and

disabling, breaking, or disconnecting cables and other hardware devices.

• A hacker may also climb a utility pole and disconnect telephone lines or

television cables, thereby disrupting service to users in the neighborhood.

Firewall Basics

A firewall is a combination of software and hardware that decides what kinds

of requests and what specific data packets can pass to and from a computer or

a local network.

A firewall for a personal computer is normally fully implemented by

software, whereas a small network of computers often found in a home

(typically consisting of 2–3 computers and a printer) may use a hardware

firewall that’s built into the network’s router.

The main task of a firewall is to block certain requests for data transfer, and

the firewall makes these decisions based on rules.

A firewall starts with some built-in (default) rules, and its user/owner can

add, delete, and modify rules.

We can say that a firewall enforces an access policy through the rules, and a

rule tells the firewall what properties of a data packet to examine and how to

decide whether to let the packet through or not.

A typical firewall performs the following tasks:

1. limit incoming data, so that data coming from certain senders (or that has

certain properties) will be blocked,

2. limit outgoing data, so a program will not be able to send data outside (to call

home) without the owner’s knowledge,

3. generate and save a log of all its activities, especially on data packets it has

blocked, and

4. do all this fast and be transparent to the user.

A firewall rule specifies a set of conditions and what action to take when a

condition occurs. A complex rule can check several conditions, while a

simple rule is limited to just one condition. Rules can also be hierarchical.

In such a case, each rule is simple and checks one condition, but a rule can

have several child rules, each checking one condition. This way, each rule is

simple, but the overall performance can be complex.

A sophisticated firewall may maintain simple statistics on the data packets

that satisfy each rule.

When a packet satisfies a rule, its idle time is set to zero, its match count is

incremented by 1, and its byte count is incremented by the size of the packet.

Such statistics can be useful to the computer owner and to the network

administrator, and can also be used in rules.

For example, if a rule hasn’t detected data from a certain sender within a

specified idle time, the action of the rule is executed (even though no data

packet has been received) and may send a probe to the sender or may alert the

user that the sender isn’t responding fast enough.

Examples of actions are ―delete,‖ to delete a data packet, ―pass,‖ to let it

through (into or out of the computer), ―drop,‖ to drop the connection (I case

of a DoS attack that tries to hang up the connection), and ―log,‖ to log the

data packet and then apply the next rule to it.

(For incoming data packets, the ―drop‖ action sends a TCP RESET command

to the sender, while for an outgoing packet the same action sends a small TCP

FIN packet.)

A modern firewall may also include rules for checking the data of a data

packet, not just the fields of its header.

This useful feature is referred to as content filtering. The user may instruct

the firewall to block all incoming (and perhaps all outgoing) data packets that

contain a certain string of characters.

This can block common viruses and worms that have already been detected

and analyzed.

An advanced firewall should also be able to recognize ethernet hardware

addresses (the so-called MAC addresses), so that the rules would be able to

distinguish between outside traffic and local traffic.

Another advanced task is to limit the amount of data (the bandwidth)

allocated to certain users or to certain applications. This way, a firewall can

help in bandwidth management

Other threts:

Router attacks

A router is an important component of a computer network, even a small

network used in a home. Even if there is only one computer, a router is still

useful.

Routers are designed to be easy to use, which also makes them vulnerable to

attacks. This has been realized back in 2006, and has been exploited by

wrongdoers since (and perhaps also before).

Perhaps the simplest attack on a router is to change the DNS server it uses.

Every time the computer user wants to connect to the Internet, the

URL typed by the user has to be translated to an IP address. There are many

DNS servers that maintain lists of pairs (URL, IP), and they supply the

needed IP addresses.

Sending the router to a malicious DNS server can be the key to a whole slew

of other attacks.

When a router, used or new, is set for the first time before it is used, the user

should do the following:

Reset the router (even a brand new one) to its factory state.

Update the router with the latest firmware available in the manufacturer’s

website.

Change the default password to a new, secure one.

The router may have features to support devices that you don’t have.

Turn those features off.

Turn off all features that allow the device to be administered from anything

other than the device(s) plugged directly into the router.

The URL-shortening threat

There are many sites and even more files. Each file on the Internet (as also on

a computer) must have a unique name, which is why many URLs are long.

Special

URL-shortening services exist to alleviate this problem. Examples are

tinyurl.com, bit (.ly), and is (.gd).

These services are useful but they also pose a security threat. Someone sends

you a short URL that should take you to an interesting site whose URL is

long. Instead, the short URL takes you to an infected website.

This threat can be prevented by checking a short URL before using it.

Website http://longurl.org/ does just that. You paste a short URL, the free

service checks it and lets you know where this URL really takes you.

There are also many Twitter clients, such as TweetDeck and Mixero, that

have a preview function that shows the long form of a shortened URL. Such

services illustrate the compromise between security and convenience.

It takes time to check a short URL, but this is time well spent.

Flash weakness

Adobe Flash is a popular multimedia application for adding animation and

interactivity to Web pages.

Originally designed and implemented in 1996 by Jonathan Gay who called it

SmartSketch, the program was acquired by Macromedia in the same year and

its name changed to Flash. Since 2007, it has been developed and distributed

by Adobe Systems.

Flash is commonly used to create animation, advertisements, and other

videos that are included inWeb pages. In July 2009, a weakness (that became

known as zero-day vulnerability) was discovered in Flash player versions 9

and 10 by an anonymous hacker. This became public knowledge, and was

exploited by other miscreants.

This weakness makes it possible to include a malicious, specially-constructed

Flash video in a Web site, such that simply surfing to the site causes harm.

The user does not even have to click on anything; as soon as the video comes

up it releases its payload.