I'm running a web site with a forum where one small part is open for posting from unregistered users. The site uses captcha, but still some spam posts get through every day. Here is the thing. All of the messages follow the same pattern, but all also come from different IP's. That makes me thing this is some sort of automated scripted "attack" from a botnet of some sorts.

The strange thing is that all the messages start with six random characters and contains a couple of links. The words have no meaning and the domains in the links does not even exist.

Why would anyone use time and resources spreading these things? Below you can see two of these messages:

A5Zfs6 exrzvrbspntz, [url=http://nktqoqllnuab.com/]nktqoqllnuab[/url], [link=http://wtrenldadvsy.com/]wtrenldadvsy[/link], [http://rnlrqfgdvdot.com/]

O2oLpL nqeffxhryfdk, [url=http://jutyurbpfxow.com/]jutyurbpfxow[/url], [link=http://jpcdtmdalpow.com/]jpcdtmdalpow[/link], [http://qopqwqxwjdjx.com/]

Since all the messages come from different IP's I can't see blocking those will help much. For now I'm considering just dropping all messages following this pattern since it's quite easy to match with a regexp.

Have anyone else seen these kinds of messages or know the point of posting them?