According to Sophos, more than 50 percent of spam today is being sent out by zombies, also referred to as "bots" (short for robot). These "bots" are controlled remotely by hackers allowing them to send spam through infected PCs or launch email-based DOS attacks.

Sophos recently announced a "zombie alert" service, wherein a client is notified if there are infected IP addresses within its network. This service advises subscribers when any computer on their network is found to have sent spam to Sophos' global network of spam traps.

"What will happen is when we see spam anywhere, we will know where it's coming from. The service will inform the network administrator about infected IP address," said Charles Cousins, Sophos managing director for Asia Pacific.

"For a lot of network administrators, it is relatively easy to spot PCs sending out high-volume emails. But what won't look unusual would be PCs sending spam in low volume every five to ten minutes," Cousins added during a recent interview with Computerworld Philippines.

The service was launched almost two months ago in the U.S. and Sophos is now promoting it in Asia Pacific. This service suits large enterprise users using fixed IP addresses, rather than dynamic IP addresses usually assigned by ISPs, and with a network of remote users.