The matrix has you. Those four words?which appeared on the retro computer screen of Keanu Reeves's character, Neo, in the 1999 hit movie The Matrix?have resonated with hackers around the Internet. No wonder, then, that a technology for taking control of a user's computer, more often than not for malicious ends, echoes the reality behind those words. Just as Neo had to come to grips with the fact that the world as he knew it was a well-crafted simulation, computer users today have to watch out for programs, known as rootkits, that attempt to take over a computer that appears normal. Rootkits are all about stealth: In the past, such programs have replaced common commands with their own modified versions. When the user of an infected computer connects to the Internet using Microsoft Windows' network driver, the system might instead route data through a malicious driver that also copies any important data?such as usernames and passwords?to the attacker's servers.