Well I'm glad I mentioned that unsolicited pop-up dealie yesterday, because a
forum comment made it clear that what I was suffering from was not a scumware
situation, but rather a method for exploiting an internal Windows service. Thankfully
indiv posted a link to the Stop Messenger
Spam website, which clearly explained the problem, and how to solve it.
Well, it's secure enough to make connecting to an IRC server a 5 minute struggle for me. Zonealarm is probably the best personal firewall, based on my own experience. Once it's been set up, it's a very useful tool.