Microsoft says, Backdoor Trojans are the Biggest Windows Threat..

Zombies continue to be the biggest threat to Windows security, Microsoft said Monday. During the six months from January to June 2006, over 43,000 new variants of so-called "backdoor Trojans" were discovered.

Additionally, the company said at least 50 percent of the computers it cleaned during the period with the Microsoft Malicious Software Removal Tool contained at least one backdoor Trojan. While this may seem quite high, it was a decrease from last year's 68 percent figure.

Behind the backdoor Trojan, the second biggest threat was the keylogger, with 27,154 variants discovered. This was followed by the downloader with 13,039 variants, the regular Trojan with 4,497 variants, and the mass mailer with 3,426.

"Backdoor Trojans and bots continue to comprise a significant percentage of the malicious software detected by Microsoft anti malware offerings and therefore serve as a top threat to consumers and businesses alike," Microsoft said in the report.

Although rookits have received a lot of attention in recent times due to Sony's use of the malware to protect its music CDs from illicit copying, their usage continues to be rare. In fact, attacks decreased 50 percent during the period and were ninth overall in rate of occurrence.