This is a quote from the book "The Gentleperson's Guide To Forum Spies" by Cryptome.org
... COINTELPRO Techniques for dilution, misdirection and control of a internet forum..
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There are several techniques for the control and manipulation of a internet forum no matter what,
or who is on it. We will go over each technique and demonstrate that only a minimal number of operatives can be used to eventually and effectively gain a control of a 'uncontrolled forum.'
Technique #1 - 'FORUM SLIDING'
If a very sensitive posting of a critical nature has been posted on a forum - it can be quickly removed from public view by 'forum sliding.' ...