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The Velocity of Censorship:High-Fidelity Detection of Microblog Post Deletions
Tao Zhu Independent ResearcherDavid Phipps Bowdoin CollegeAdam Pridgen Rice University
Jedidiah R. Crandall University of New MexicoDan S. Wallach Rice University
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March 2006
July2009
http://en.wikipedia.org/wiki/Microblogging_in_China
August2009
Microblogging sites in China
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Sina Weibo
● 503 million registered users as of Dec 2012.○ More than half are from mobile devices.
● About 100 million messages are posted each day on Sina Weibo.
● Promote visibility of social issues.
http://en.wikipedia.org/wiki/Sina_Weibo
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Weibo’s influence:Wukan incident - 2011
乌坎 (The village name) vs 鸟坎 (Neologism)
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Sina Weibo
● Strict controls over the posts.
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Introduction of our research
● Detecting a censorship event within 1-2 minutes of its occurrence.
● Three strategies Weibo system uses to target sensitive content quickly.
● Performing a topical analysis of the deleted posts.
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Methodology
1. Identifying the sensitive user group
2. Crawling posts of sensitive user groups
3. Detecting deletions
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Identifying the sensitive user group
● Use outdated sensitive keywords from China Digital Times
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● Identifying the sensitive user group○ Use outdated sensitive keywords from China Digital
Times.○ Start with 25 sensitive users.
Repost
Identifying the sensitive user group
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● Identifying the sensitive user group○ Use outdated sensitive keywords from China Digital
Times.○ Start with 25 sensitive users. ○ Sensitive group reaches 3,567 users after 15 days. ○ More than 4,500 deletion daily
Identifying the sensitive user group
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● User timeline: ○ Weibo user timeline API returns the most recent 50
posts of the specified user.
○ Query 3,567 sensitive users once per minute■ 100 accounts for API call■ 300 concurrent Tor circuits.
○ Four-node cluster running Hadoop and Hbase■ 2.38 million posts from July 20 to September 8,
2012.
Crawling
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Diff
Our databaseLatest 50 posts Deleted Post
Detecting deletions
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t0 t1 t2 tn
The lifetime of deleted Post = tn - t0
Detecting deletions
…...
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● Permission-denied or system deletion○ “Permission denied” error.○ Caused by censorship events.○ The post still exists but cannot be accessed by users.
● General deletion○ “Post does not exist” error.○ May caused by user self deletion or censorship
events.○ The post does not exist.
Detecting deletions
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Detecting deletions
1
2
Permission-denied deletion 4.5%
General deletion8.3%
2.38 Million user timeline posts
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● Permission-denied deletion or system deletion
■ Around 1,500 permission denied deletions.
■ Comparing with WeiboScope, which is tracking around 300,000 users and have no more than 100 permission denied deletions daily.
Detecting deletions
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Distribution of deleted posts
Whole lifetime First two hours
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Strategies to target sensitive contents 1. Weibo has filtering mechanisms as a
proactive, automated defense.
2. Weibo targets specific users, such as those who frequently post sensitive content.
3. When a sensitive post is found, a moderator will use automated searching tools to find all of its related reposts, and delete them all at once.
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1. Keywords list filtering
● Weibo has filtering mechanisms as a proactive, automated defense
○ Explicit filtering
Sorry, The content violates the relevant
laws and regulations. If need help, please contact customer service.
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● Weibo has filtering mechanisms as a proactive, automated defense
○ Explicit filtering○ Implicit filtering
1. Keywords list filtering
Your post has been submitted successfully. Currently, there is a
delay caused by server data synchronization. Please wait for 1 to
2 minutes. Thank you very much.
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● Weibo has filtering mechanisms as a proactive, automated defense
○ Explicit filtering○ Implicit filtering○ Camouflaged posts
1. Keywords list filtering
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● Weibo has filtering mechanisms as a proactive, automated defense
○ Explicit filtering○ Implicit filtering○ Camouflaged posts○ Surveillance keywords list ?
■ If no such list the cost will be too expansive● Suppose to censor 70,000 new posts in one minute, it needs
1400 simultaneous workers (50 posts per minutes per worker).
● Assuming 8 hour shift, 4200 works is required. ● It is not cost efficient
1. Keywords list filtering
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2. Targeting specific users
● Weibo targets specific users, such as those who frequently post sensitive content.
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3. Finding all related reposts
● When a sensitive post is found, a moderator can find all of its related reposts, and delete them all at once
Standard deviation (minutes)
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Censors work in the night
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Censors catch up on overnight posts by late morning
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Conclusion
Whole lifetime First two hours
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Thank you!
Q & A