Shoutbox

As foaly said, at one point an unpatched XP or 2000 could be compromised in a matter of minutes by someone using a tool to scan the Blaster or Sasser ports, as these exploits were remotely available and could do some serious damage.

Basically, you could plant a file on the computer, set it to run at start up, set the computer to reboot (usually done by causing an "essential" system service to crash) and then you could use the program as you saw fit (if it was something like sub7 or whatever).

In certain machines, you could likely overclock the hardware and permanently damage it. Newer CPUs and Graphics cards would be most at risk.

Currently there aren't any widely-known exploits for Windows XP SP2 + Patches (and when there are, MS usually release patches quickish) so it'll take a lot longer for a PC to be exploited, if it's not in use.

The amount of viruses on a system is usually proportional to the users age (teenagers tend to use things like Limewire to download files, and have no idea that the really small download for the latest hit is actually a virus) and noobishness (even an older person is likely to click "Protect Yourself Now!" in an advertisement).