If you run a site where you allow people to post content or add comments to stories, chances are you've run into comment spammers. These are black hat marketers that try to embed links on your site to their properties either for the traffic or to get the links for SEO purposes.
There is a really great, totally free plugin called Akismet you can use on most open source systems like WordPress and Drupal. Details are here. Akismet looks at comments to see if they match certain spam profiles and if so will hold them in moderation for you in a separate area where you can bulk delete them. I'be been using this for a while now on my wordpress sites and find it really makes it a lot quicker and easier to deal with this kind of spam.
Oh, and don't forget to report content spammers to Google.