Filtering the Anonymous USENET Trolls?

BoneFlower asks: "Anonymous remailers are all well and good, but sometimes people use them to abuse people through email or through trolling newsgroups. I've had limited results filtering "anonymous" on a USENET group I frequent but many anonymous remailer trolls get through. The group was nearly unuseable for over a week due to the volume of anonymous remailer trolls. Does anyone have tips on filtering them out? I personally use Forte Agent 1.9.1, many others use Netscape/Mozilla, OE, and various others. If you could help us out, we'd appreciate it."