Security tools have found 16 million pieces of malicious software on Windows computers over the past 15 months, research released by Microsoft has revealed.
The report on malware found on 5.7 million machines is based on the data collected by Microsoft’s Windows Malicious Software Removal Tool, which was first launched in January 2005.
It shows the tool has been used approximately 2.7 billion times on at least 270 million computers. It has removed at least one malware item from every 311 computers it runs on.
Backdoor Trojans, which allow attackers to control infected computers and steal confidential information, are “a significant and tangible threat to Windows users”, the research says. Backdoor Trojan’s were present on 62% of the computers infected with malware, with bots making up the majority.
Rootkits, which make system changes to hide other possibly malicious components, were “a potential emerging threat but have not yet reached widespread prevalence”, the report says, with rootkits found on 14% of infected machines. But this figure drops to 8% if WinNT/F4IRootkit, the controversial rootkit distributed on Sony music CDs as an anti-copying measure, is excluded.
Worms spread through email, peer-to-peer networks and instant messaging had hit 35% of the infected machines.
The forthcoming Windows Vista is set to include beefed up security systems, but analysts warned last month that users may be annoyed by the intrusive and repetitive effect of the new features.