Messaging security company CipherTrust says it is seeing a massive growth in the number of PCs that have been hijacked by malicious hackers.
On Tuesday, CipherTrust reported a 23 percent growth in the total number of zombie PCs detected this week alone, due, they said, to the release of a modification of the Mocbot worm.
The company said it has identified an average of 265,000 zombies per day since the release of the Mocbot worm, which exploits the MS060-040 Windows vulnerability that was first announced on 8 August.
The Mocbot worm infects machines through flaws in Windows and Microsoft Office applications. Any computer infected by the worm will become part of a large network, which can be controlled remotely to carry out tasks such as sending masses of junk mail.
In June, Microsoft warned that the threat posed by botnets and zombies was growing fast.
Ed Rowley, technical consultant at CipherTrust, said that zombies accounted, in part, for the large increases in spam that many security companies have been reporting.
"Mail volumes have once again reached a high this week, with spam making up 81 percent," he said. "Much of this increase… can be attributed to the new zombies unleashed by the Mocbot worm."