Turns out the problem goes even deeper

Quote:Profile Signature Spam

Linking to external spam urls from the user profile page

This is the latest an probably the most difficult spam problem that I have had to deal with. It’s a rather clever trick that spammers came up with to improve their site’s search engine performance and get better search traffic. Spammers sign up for dozens of accounts using keywords like “Buy DrugX Here”, where DrugX is replaced with a variety of prescription drug names. They then place as many links as they can fit in their user signature directing to their sites. The reason that spammers have been using this method is because my site is seen as reputable through the eyes of Google, so placing text on my site for the traditionally disreputable pharmaceutical drug websites gives more credibility and they often appear high up on search results because of my vBulletin SEO methods (Thanks to vBSEO).

What’s so tricky about this problem is that there’s really no way to easily see when a user is doing this, unlike traditional thread or post spam that appears on the general forum where users will often flag it. The only way to check for this type of spam is to go through each days user registration log looking for suspicious names.

So until we crack this nut (feel free to help!) I disabled Signatures for all "normal" users