Microsoft Windows Vista operating system took some of its first punches when a dangerous vulnerability was disclosed earlier this month, but the OS held strong, a security analyst said at the InfoSecurity Europe (Infosec) conference in London.

At least two exploits were targeted at Vista, trying to circumvent a new security feature designed to thwart malicious software attacks, said Mikko Hypponen, chief research officer for F-Secure.

Microsoft issued an out-of-cycle patch for the vulnerability, which occurred in how Windows processed ‘.ani’ or animated cursor files, which allow websites to replace the regular cursor with cartoonish alternatives.

At least two exploits tried to take advantage of the vulnerability, by skirting Vista's Address Space Load Randomization (ASLR) security feature, which varies how the OS's memory map looks each time the computer is booted, Hypponen said. The feature can confound some malicious software programs, which need to run in a specific part of the computer's memory to function properly.

Both of the exploits attempted to circumvent the feature and insert themselves into memory. Neither worked and merely caused the computer to crash, Hypponen said.

A Microsoft security executive said he was unaware of specific animated cursor attacks against ASLR, but it shows that Vista's security is working as designed.

"I'm happy they [F-Secure] showed that it works," said Roger Halbheer, Microsoft's newly appointed chief security advisor for Europe, the Middle East and Africa.

The animated cursor vulnerability is especially dangerous since a machine could become infected if a user just views a malicious website. It was the third zero-day vulnerability Microsoft had patched off schedule since January 2006.

Windows Vista is likely to come under increasing attacks as it's more widely adopted, Hypponen said. About 3 percent of US consumers are currently using Vista, with about 79 percent still running Windows XP, according to recent statistics cited by Hypponen from Harris Interactive. PC Advisor readers have also reported a fairly high take up of Vista in the UK.

Vista's security improvements mean a machine can be connected to the internet in its default configuration without any third-party security products and be fairly protected, Hypponen said. But just as security vendors had to revamp their software for Vista, so will the malicious software writers, Hypponen said.

"Unfortunately, it will change, and it will change for the worse on the Vista side," Hypponen said.

See PC Advisor's review of Windows Vista and discuss the new operating system with other readers in our Windows Vista forum.