Editing Anti-spam techniques (section)

===Checksum-based filtering===
''Checksum-based filter'' exploits the fact that the messages are sent in bulk, that is that they will be identical with small variations. Checksum-based filters strip out everything that might vary between messages, reduce what remains to a [[checksum]], and look that checksum up in a database such as the  [[Distributed Checksum Clearinghouse]] which collects the checksums of messages that email recipients consider to be spam (some people have a button on their email client which they can click to nominate a message as being spam); if the checksum is in the database, the message is likely to be spam. To avoid being detected in this way, spammers will sometimes insert unique invisible gibberish known as ''[[hashbusters]]'' into the middle of each of their messages, to make each message have a unique checksum.