Microsoft's Windows Vista OS has already failed a major security test.

Independent security certification body Virus Bulletin has revealed that Microsoft's much touted antivirus product, Live OneCare, is one of four similar products that failed to reach the required standard.

Eleven of 15 products submitted passed the stringent tests.

Virus Bulletin's VB100 pits antivirus packages against a spectrum of known viruses. Products must detect every virus, but declare no 'false positives'.

Vista is, of course, a brand-new product, but a Virus Bulletin spokesman said that this is 'no excuse'. He cited the lengthy delays in Vista's development, and suggested that companies shouldn't put forward antivirus tools for testing if they weren't ready.

Vista's improved security is one of its major selling point, and antispyware in particular has been boosted. But experts believe that additional antivirus protection is required.

Virus Bulletin tests products free of charge. Crucially, it does not permit re-testing, so vendors have to get their products right first time. To see the full results of the Virus Bulletin tests, click here.

McAfee's VirusScan was another big-name failure of the VB100 certification process. However, when PC Advisor spoke to the company it told us that it is aware of Virus Bulletin's VB100 test results for McAfee VirusScan Enterprise 8.5 and is working with Virus Bulletin on a 'discrepancy' in the test results.

According to McAfee, Virus Bulletin has accepted that it was not using the latest antivirus updates available at the time of test, which caused McAfee VirusScan Enterprise 8.5 to fail when detecting the test viruses. McAfee is currently working with Virus Bulletin on this discrepancy and to make the updated test results available.