Microsoft's Windows Live OneCare security suite has failed a test to detect or stop 37 malicious programs on Windows Vista.
Independent security certification body Virus Bulletin tested 15 security suites on Windows Vista against a set of malware from the WildList database.
"The tests conducted in our secure labs were against the most significant viruses and worms affecting real-world users," said John Hawes, technical consultant at Virus Bulletin.
"In these days of hourly updates, it is always a surprise and a disappointment to see major products missing them. Computer users deserve to see a better performance than this from security vendors."
OneCare detected about 99.91 per cent of the threats, picking up on all macro viruses. But it failed to stop some viruses, file infectors and polymorphic malware which constantly changes in an effort to avoid detection by security software.
Microsoft's offering was one of four suites which failed to pass the Virus Bulletin test. The others were G-Data AntiVirusKit 2007 v.17.0.6353, McAfee VirusScan Enterprise 8.1i and Norman Virus Control 5.90.
Redmond unveiled version 1.5 of OneCare last week which added support for Vista, as well as unified virus and spyware scanning and more flexible back-up options.
The vendor also used the launch to introduce the suite in 16 countries including the UK, Germany and France.
Microsoft said in an emailed statement that it is looking at Virus Bulletin's research methodology and its results.
The company is working "to ensure that Windows Live OneCare performs better in future tests and, most importantly, to continually enhance OneCare to ensure the highest level of protection and service that we can provide our customers".
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