Allows an administrator to ban certain words from comments. This can be a very simple but effective way of stopping spam; just add "viagra", "porn", etc to the banned words list.
Regex bans are also supported, allowing more complicated
/http:.*\.cn\// to block links to
chinese websites, or
to block comments with four (or more) links in.
Note that for non-regex matches, only whole words are matched, eg banning "sex" would block the comment "get free sex call this number", but allow "This is a photo of Bob from Essex"