Love or hate its nagging prompts, Vista's Account Control feature (UAC) has a security feature that marks it out from any other type of Windows security programme -- it can spot rootkits before they install.

This is one finding buried in a report published in two German computer magazines some months ago after testing by the respected AV-Test.org, which set out to find out how well anti-virus programmes fared against known rootkits.

The answer was not particularly well at all, either for Windows XP, or Vista-orientated products. Of 30 rootkits thrown at XP anti-malware scanners, none of the seven AV suites found all 30, a similar story to the six web-based scanners assessed. Only four of the 14 specialised anti-rootkit tools managed a perfect score.

The best of the all-purpose suites was Avira AntiVir Premium Security Suite, which found 29 active rootkits, with Norton finding as few as 18. The anti-rootkit tools fared better, with AVG Anti-Rootkit Free, GMER, Rootkit Unhooker LE, and Trend Micro Rootkit Buster achieving perfect scores. The scores for removal were patchy, however, with all failing to remove any of the rootkits they had found.

The results for Vista products were harder to assess because only six rootkits could run on the OS, but the testers had to turn off UAC to get even this far. Vista's UAC itself spotted everything thrown in front of it.

Only three of the 17 AV tools for Vista managed to both detect and successfully remove them, F-Secure Anti-Virus 2008, Panda Security Antivirus 2008, and Norton Antivirus 2008.

Once on a PC, rootkits can bury themselves quietly, but they have to get to that point first. As long as users interpret prompts from the UAC system attentively, or those messages haven't in some way been spoofed, rootkits struggle to jump to the PC without drawing attention to themselves.

That UAC can tell a user when a rootkit is trying to install itself is not in itself surprising, as Vista is supposedly engineered from the ground up to intercept all applications requests of any significance.

Rootkits matter. By their nature, they set out to bypass the operating system. Once installed, they can do whatever they like, including loading other malware from a position of privilege. The question is, how can one be sure that a scanner is spotting a type of program built on the principle of extreme stealth?

An interesting footnote to the XP rootkit testing was that the samples chosen included three 'professsional' rootkits, apparently legitimate programs designed to enforce things such as copy protection. The most infamous example of this category included is the Sony XCP/First4Internet rootkit, which caused the company so much embarrassment when it was discovered in 2005.

But in a period of weeks when Vista has received criticism for its rate of vulnerabilities, Microsoft's programmers can at least point to evidence that UAC is efficient at stopping those infections from happening automatically.

The test, Anti-stealth Fighters: Testing for Rootkit Detection and Removal, was republished in the April issue of Virus Bulletin.