Good news for users of Windows Vista. According to figures compiled by PC Tools, the OS has experienced only slightly more vulnerabilities than Windows 2000, which appeared eight years ago when malware was far less common.

Or is that the bad news? Despite having a reputation as the least vulnerable of Microsoft's operating systems, Vista still managed to record 639 unique vulnerabilities over roughly the last half year, which puts it in a worse position than the aging Windows 2000, which experienced 586 over the same period.

Windows XP, which still accounts for the overwhelming volume of the Windows user base, had 1,021, with Windows 2003 Server reaching 478.

The Australian security company collected statistics on the number of infections by analyzing figures from anonymous users of its ThreatFire community, with vulnerabilities double-confirmed by third-party anti-virus engines. The numbers are per 1,000 machines on each platform.

"Microsoft has invested a great deal in making Vista more secure, by providing a number of security enhancements which were not in prior Microsoft operating system releases," concluded PC Tools CEO, Simon Clausen. "But industry experts have been reluctant to confirm its improved resistance to malware with good reason."

"Since its launch, Microsoft has flagged the increased level of protection Vista provides as one of the key reasons why consumers should upgrade from Windows XP to Vista. If Microsoft's forecasts for the operating system are correct and Vista's market share increases significantly, we could expect infection rates to increase further on Vista," he added.

The problem with these bare statistics is that they make no mention of how serious these vulnerabilities were -- Vista has recorded few that come into the 'most serious' category by comparison with XP. They also don't specify where the vulnerabilities were uncovered. The majority of vulnerabilities are not in the OS itself and are traced to problems in browsers, for instance, and can even apply across platforms.

Microsoft would also point out that the user access control (UAC) feature of Vista stops malware from exploiting the OS without the user at least being aware that something is happening. Windows 2000 and XP lack even this basic level of protection.

On the other hand, Vista has had its embarrassing moments, securitywise. Only weeks ago, Microsoft had to explain how the .ANI animated cursor bug was allowed to find its way into Vista code without being patched as part of the much-vaunted Security Development Lifecycle (SDL).