A Microsoft executive Wednesday said Windows Vista's first 90 days was a huge security success when compared to the opening three months of Windows XP, the current Apple Mac OS X, and three flavours of Linux.

Jeff Jones, the strategy director in Microsoft's security technology unit, tallied up vulnerabilities patched during the first 90 days of Vista, XP, Mac OS X 10.4, Red Hat Enterprise Linux 4 Workstation, Ubuntu 6.06 LTS, and Novell SuSE Linux Enterprise Desktop 10.

He gave Vista the checkered flag.

"Vista has an improved security vulnerability profile over its predecessor, and a significantly better profile relative to comparable modern competitive operating systems," Jones asserted in his blog. By his count, Vista has been hit by just one vulnerability since its introduction to enterprises at the end of November. The bug, which was in the anti-malware scanning engine used by the bundled-with-Vista Windows Defender, was patched last month.

By comparison, said Jones, in their first 90 days, Windows XP was nailed with 14 bugs, Mac OS X 10.4 (Tiger) with 20, Red Hat with 137, Ubuntu with 71, and SuSE with 80.

Even when vulnerabilities that were disclosed but not patched are added in, Vista still comes out far ahead. Its five total bugs -- one patched, four made public but not fixed as of Feb. 28 -- compared favourably with XP's total of 18, Mac OS X's 27, Red Hat's 201, Ubuntu's 100, and SuSE's 111.

"As an early and tentative indicator, this is good news for Windows Vista security," said Jones in a report he issued of his findings (download PDF).

But simply counting up vulnerabilities, patched or not, doesn't tell the whole story, argued Oliver Friedrichs, senior director of Symantec's security response team.

"The severity of [a] vulnerability plays into this, too," Friedrichs said Thursday. "A single vulnerability that has a high severity could lead to the next Sasser or Blaster [worm], but an OS with a larger [bug] count, but with [ones rated] less high may be in a better defensive position overall."

Likewise, Friedrichs said, comparing Windows to any other operating system is always dicey because of the overwhelming market share Microsoft's products enjoy. That means flaws in Windows are much more likely to be exploited by attackers.

"A high-severity vulnerability may not receive widespread exploitation on another OS," Friedrichs said. "That's not uncommon. It doesn't diminish the criticality of the vulnerability itself, of course. For that vendor's customer base it does present a serious risk, but the overall risk to the Internet may not be much."