Redmond estimates 1.5 million users downloaded its freebie security scanner software during its first week of availability earlier this month.

Microsoft Security Essentials, which comes at no extra charge to consumers running kosher versions of Windows, detected four million instances of malware of one type or another on 535,752 distinct machines in its first week of operation up from its release on 29 September until 6 October. Windows XP machines were more likely to be infected than Vista boxes which, in turn, were more bug-filed than Win 7 machines.

A blog posting from Microsoft containing pie-charts illustrating malware infection instances can be found here.

Independent reviews from the likes of AV-Test.org gave Microsoft Security Essentials a positive reception. Microsoft's freebie software earned favourable comparison with other free packages, such as AVG and Avast, in detection rates and scan speed. The avoidance of false positives was a plus for Redmond's effort, while the lack of effective behaviour-based malware detection was the one big minus in comparison with AVG.

AVG boasts a user base of 80 million, according to company estimates. However, user dissatisfaction with the tendency towards bloatware that came with AVG 8 make it vulnerable to attack from the likes of Avast and Avira, as well as Microsoft, which boasts a huge name recognition advantage in the consumer market. ®

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