I agree, while at Georgia Tech I had the misfortune of a computer crash and still had a chance to recover my data. I then reformatted my computer and began to reinstall windows. I had to leave for class before the install was complete, so I didn't have a chance to install my firewall (which is my first step after reinstalling).
The funniest part was I forgot to unplug the network cable from my computer and by the time I got back my computer had been infected by a trojan, which was attempting to replicate itself on the Georgia Tech network.
Well, this is against the Georgia Tech AUP so my connection to the internet was blocked. I had to reinstall again with the network cable unplugged, get my firewall installed, and then call OIT to get my connection to the internet reestablished.
My estimate of how long it took my windows installation to be compromised was roughly 20 minutes.
This article backs up my estimate (not that I trust CNet on a very regular basis)
I'm a unix admin at a campus and had a case where I had a lab full of PCs a few years back. I had a spare hard drive in case I needed to do a quick drive swap on a boxthat had Win 2000SP4 on it, and the replacement drive had 2000SP1. In the time it took for the machine to BOOT, it got hacked, trojaned, and rebooted. I was very much impressed and disappointed, all at once. That was FAST!