OK - didn't get much done today after all (day is not done yet though). I spent today working to fix my son's machine - 15 viruses, 95 different malwares, adware, etc. Our internet access was grinding to a halt, so I put a log onto the router and found out that his machine had been zombied - it was looking for open IP addresses to cause even more trouble. I ran Ad-Aware first, and didn't find any more than the usual suspects. Then I ran Spybot Search & Destroy, which found a few things - maybe about 3 or 4, but nothing that I hadn't seen before. Then I installed Spyware Doctor and this discovered about 95 different malware variants. I thought that this had killed the zombie problem, so I went back to work. A little later I noticed that the zombie was still quite alive, so finally I ran Norton Antivirus. This discovered a host of problems, some of which I am still dealing with. I am pretty sure that one of these is the problem, but if it isn't the only thing left is to wipe the disk and start over.
The moral is... don't let teenagers have access to the net.