Even if the system administrators can trace the attacks, what they find is merely another victim - the zombie computer, not the evil master.

In most instances, the user of a zombie computer is never aware that it has been commandeered.

One case under investigation, officials say, may involve as many as 300,000 zombie computers.

Appropriate the compromised machine as a zombie computer for attacks on other computers.

Machines that suddenly start sending lots of e-mail may well have become zombie computers.

Most owners of zombie computers are unaware that their system is being used in this way.

These zombie computers were often employed as a response to anti-spam laws and spam filtering.

Most owners of zombie computers do not know that their system is being used in this way.

Allegedly, one hacker under investigation used a single computer to control a network of more than 1.5 million zombie computers.

You're a zombie computer that's been taken over.