There's another handy plugin: Akismet.

Akismet is a plugin which was originally written for Wordpress Blogs and it compares comments to known spam and puts them in the moderation list if it suspects spam.
You need to register an account with Wordpress to get a working API key.

Once you have that key, you can obtain a modification of the plugin which acts as a vBulletin hack:
Vbulletin - Akismet Antispam

Once set up with the API key working it will put any suspicious posts into Threads Awaiting Moderation.