Okay, Windows experts stand aside, you all likely had this one licked long ago.
All others -- that is, anyone that's endured Windows Messenger Service pop-up spam, but didn't want to pay one of the spammers that have been abusing your Windows Messenger Service security vulnerability to stop spamming you -- read on.
I can't believe that for the past five and a half months I've allowed Messenger Service Pop-Up Spam to show up on my Windows 2000 Server. I'd kept simply hitting the close-box of each Messenger Service message that showed up.
It wasn't until today that I decided to do a quick Internet search to learn more about this rude spam mechanism that I kept thinking Microsoft would put a stop to with a patch or an update.
I put a stop to it. See my Computer FAQs entry titled "How-To Stop Windows Messenger Service Pop-Up Spam" to see what it took. (It's really very easy, just 4 steps.)