A cancelbot is an automated or semi-automated process for sending out third-party cancel messages over Usenet, commonly as a stopgap measure to combat spam.
[1] One of the earliest uses of a cancelbot was by microbiology professor Richard DePew, to remove anonymous postings in science newsgroups.
[2] Perhaps the most well known early cancelbot was used in June 1994 by Arnt Gulbrandsen within minutes of the first post of Canter & Siegel's second spam wave,[3][4] as it was created in response to their "Green Card spam" in April 1994.
Cancelbots must follow community consensus to be able to serve a useful purpose, and historically, technical criteria have been the only acceptable criteria for determining if messages are cancelable, and only a few active cancellers ever obtain the broad community support needed to be effective.
This allows administrators to decide which reasons for third-party cancellation are acceptable for their site: