I realize this is a pretty vague question, but I occasionally get spam messages through my contact form on a Drupal 6 site. The contact form does not have any anti-spam protection (i.e. math question). The messages I get are all very similar and just jumbled junk, like below, so I think they're all from the same source.

Example:

ylsaf0V bpsdfuxnhjjd, [url=http://wwgfsggzgyjyjm.com/]wwgrfgzrgsjyjm[/url], [link=http://xmgvyghcuufvb.com/]xmjyhvyjyfjirovb[/link], http://frgxmdghrgruhfc.com/

Anyway, I'm just wondering what the point of such a message is. All the links are dead, it's illegible, and it's not trying to sell me a product or get me to do anything, so I'm a bit perplexed. Is there any way to tell where they're coming from? And how concerned should I be? To be clear, I'm not asking how to avoid them, I realize just adding a simple math challenge or captcha would likely do the job.