Windows/NetBIOS pop-up Spam:

bofus writes "This article from Wired News presents a new way to deliver unsolicited advertising content - the MS Windows Messenger service. It appears that the client software hasn't been widely distributed yet, but it's probably only a matter of time before a free clone is circulating. This method could become the delivery method of choice for all kinds of unsolicited junk, given the number of unsecured PCs out there. On the flip side, if you run a relatively secured machine and have some sort of firewall, this probably shouldn't concern you."