The latest tests conducted by independent anti-virus testing organisation Virus Bulletin have revealed that 12 out of 35 top security vendors are not up to the task of protecting Windows Vista.

Several big names, including CA, PC Tools and Symantec, failed the stringent VB100 test which pits security systems against the publicly available WildList of malware known to be circulating.

Products must be able to detect 100 per cent of the malware, and must not generate any false alarms when scanning a clean set of files, Virus Bulletin explained.

"The biggest issue we encountered this month was a lot of serious instability - blue screens and crashes and screens that have shut down or overheated," said test director John Hawes.

"It is hard to tell if this is the influence of Vista, but you'd rather be without anti-virus than have it kill your machine."

Most of the 12 products that failed fell victim to a polymorphic file infector, but there were also "quite a few" false positives, said Hawes.

Alongside the Vista tests, Virus Bulletin continued its new test designed to show the reactive and proactive detection abilities of anti-virus products.

Hawes said that Microsoft came out "top on the proactive side by a whisker, and pretty good on the reactive side", highlighting the significant time and resources Microsoft is putting into security under its Forefront brand.