"It only affected Windows 2000," said Stephen Toulouse, a manager at Microsoft's Security Response Center. "So far its has shown a very limited impact -- we're not seeing any widespread impact to the Internet, but we remain vigilant."
The Zotob worm installs itself into the Windows system folder as botzor.exe and alters the system's host file to prevent the user from accessing anti-virus websites. Additionally, the worm also connects to an IRC server, enabling malicious users to remotely control infected systems. More details at Reuters