I've heard that Akismet is a really good tool to use if you need to fight spam with a Wordpress blog. Anytime the topic "How do I get rid of spam on my blog" comes up, most members refer the user to Akismet. Now you wont have to manually delete hundreds of spam comments. Most of the spam will get caught and out of 200 spam detections you may only have to manually delete a few here and there.
To learn more visit Akismet forum.