A Microsoft executive said Windows Vista's first 90 days was a huge security success when compared to Windows XP, 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 top marks.

"Vista has an improved security vulnerability profile over its predecessor, and a significantly better profile relative to comparable modern competitive operating systems," Jones said 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 malware-scanning engine in 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, Vista still comes out far ahead. Its five total bugs - one patched, four made public but not fixed as of 28 February - 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 vulnerabilities, patched or not, doesn't tell the whole story, argued Oliver Friedrichs, senior director of Symantec.'s security response team.

"The severity of vulnerability plays into this, too," Friedrichs said. "A single vulnerability that has a high severity could lead to the next Sasser or Blaster, but an OS with a larger count, but with [vulnerabilities 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."

Friedrichs also questioned whether 90 days of Vista was an apples-to-apples comparison with XP or other operating systems, what with Vista's two-stage roll-out. "This [scorecard] started the day it shipped to enterprises, but they have a much much slower [Vista] adoption rate than consumers. The fact is, the installed base of Vista has not grown as quickly as did XP's in its first 90 days."

Apparently, that applies to hackers, too. "Attackers have in many cases not had ready access to the platform for the entire 90 days," Friedrichs said.

Still, Microsoft is doing something right, said Friedrichs, who pulled numbers from Symantec's recently published internet security threat report. In the last six months of 2006, Microsoft patched a sample set of 39 vulnerabilities in an average of 21 days, the fastest of a group of OS vendors that also included Sun, HP, Apple and Red Hat. Apple, for example, took an average of 66 days to issue fixes for its Mac OS X vulnerabilities, while Red Hat's average was 58 days. HP and Sun lagged far behind, with averages of 101 and 122 days, respectively.

"Microsoft was clearly the best," Friedrichs said.

Jones and Friedrichs agreed on one thing: 90 days is an awfully early spot to benchmark. "It is too soon to get a complete picture," Jones acknowledged in his report.

"The first 90 days may not be the best measurement," Friedrichs said. "With the [security] improvements Microsoft has made, we would expect that the OS is more secure. But is that meaningful in the long term?

"Hackers are moving away from attacking the core OS, and are focusing on third-party applications and third-party drivers," he said. "So in the future, though it may be likely that Microsoft will be less to blame for attacks because it's invested in [Vista's] security, the overall volume of attacks or exploits will not diminish."