New form of Spam

[yankidank]

I've been moderating a VB forum for about three years now and I've come across many types of spam that are usually pretty simple to catch and ban. I even wrote an article about how I stop vBulletin spam in case anyone is interested. Anyways, today I discovered a new method that spammers are using to get around my several spam checks and I'm trying to figure out if there's a solution to stop it.

Spammers are creating accounts and copy/pasting existing posts into their own new threads. By doing this they are getting around my safeguards that require that users have X number of posts before they can have a signature. Nobody is reporting the new spam because it looks legit, but out of context.

Is there any current mod for vBulletin that checks for duplicate content before approving a post? That sort of mod would save the day for me. Thanks for your help guys/gals.