This addon filters out messages received in whisper when detected as spam.
On a fresh install, the trusted list is empty, then filled with people in the friendlist and in your guild. When a whisper is received, suspected of spam and not in the trusted list, it is hidden and the sender receives: 'This message has been detected as spam. You have to answer to this message using the password to become trusted. The password is: ' followed by the password you set.
The addon only blocks what it thinks is spam, regular whispers are just shown as usual. When he does, he's added in the trusted list and won't see that filter ever again. The point is that goldsellers create lvl 1, spam everyone with an add and delete that char and thus impossible to blacklist them.
There are several built-in filters but you can add your own.
Command line: /taggle