The Washington Post reports:
Microsoft today gave the world a rare -- albeit conservative -- glimpse of its view on just how bad the virus and bot problem has gotten for Windows users worldwide. The data comes from 15 months' worth of experience scanning computers with its "malicious-software removal tool," a free component that Microsoft offers Windows XP, Windows 2000 and Windows Server 2003 users when they download security updates from Microsoft.
According to the article, of 270 million different computers running Microsoft's Malicious Software Removal thingamabob, 5.7 million, or about 3%, were infected with "malicious software". That's a much better rate than I would've guessed.
That's likely to be significantly lower than the actual percentage of Windows computers infected with malware, as the Malicious Software Removal Tool is only installed on computers that use Windows Update, or have regular patches applied to them by other means.
Scarily, that also means there's a small but significant chance of infections even if the computer has a reasonably current patchlevel.
