"There´s a huge number of compromised machines sitting on the Internet at any one time," he said. "In many cases, these boxes are for hire--they´re essentially owned by the virus writers and rented out to the highest bidder."

"It´s a matter of how do we reach the people who own those PCs and let them know what´s going on?" Weafer added. "It´s not just MyDoom--they´re wide open to anything attackers want to throw at them."