It's late one evening last July, and a green activity light is blinking on the front of the DSL modem next to my desk.

I'm asleep in the next room, but my computer is busy working, tirelessly handling page requests from hundreds of Code Red zombies.

Each one is hoping to find the same thing: a particular file with a particular vulnerability that just might be on my system. If the zombie discovers the file, it will exploit a well-published security hole to copy some files to my computer, install a remote control "back door," then instruct my system to begin scanning the Internet for other vulnerable systems to compromise in the same fashion.