Wednesday, July 09, 2008

COPA: how filters work


Visitors following the COPA appeal might want to read the “How Stuff Works” discussion of Internet filters here, especially Internet Censorship at Home. The two main techniques employed are blacklists (or URL’s) and keyword blocking. The weakness of these approaches, particularly with keywords, is that filters cannot discern context or intent the way human readers can. Sometimes, as with automated screening for advertisers, there is an attempt at context detection that is misplaced. For example, a discussion of how the Second Amendment should be taught in high school government might be blocked because the connection of particular subjects could be viewed as enticing – until a human being (like a teacher) can read the posting and understand the real point.

There is also some controversy of the practice by many web filtering programs of encrypting their blacklists. A sidebar in this link gives other examples of false context blocks.

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