Backdoor trojans and rootkits represent two of the fastest growing malware expunged by Microsoft's Windows Malicious Software Removal Tool (MSRT), which was unveiled in January 2005.
The software giant today released a report documenting trends in the type of malicious software cleaned by the tool in an attempt to shed light on the current threat landscape.
According to the report, the MSRT - free for licensed Windows users - has been executed 2.7 billion times by at least 270 million unique computers. It has removed malware from 5.7 million computers, or one instance for every 311 computers on which it runs.
Among the report's major findings:
- The tool removed at least one backdoor trojan each, mostly bots, from about 3.5 million computers.
- Of the 5.7 million computers on which the tool has removed malware, 62 percent contained at least one backdoor trojan.
- Rootkits were present in 14 percent of the computers on which the tool cleaned malicious software.
- Social engineering served as a major source of malware attacks. Worms spreading through email, instant messaging (IM) or peer-to-peer networks were found on 35 percent of the computers cleaned by the tool.
Backdoor trojans made up the most prevalent threat removed by the tool, followed by email worms, rootkits, peer-to-peer worms, exploit worms, viruses and IM worms, the report said.