Microsoft patched nine vulnerabilities in Windows 7 last week, five marked "critical," in a move that will require users upgrading to the new operating system to download a security update to keep their PCs secure.
The patches were the first for Windows 7's final build (dubbed RTM for "release to manufacturing"), which has been in some customers' hands - primarily enterprises with volume licensing agreements - since August.
Windows 7's patch count was significantly less than either Windows Vista's, its immediate predecessor, or that of Windows XP, the eight-year-old operating system installed on the majority of systems worldwide.
An analysis by Computerworld of the massive October 13 security update - the largest by Microsoft since it started patching on a regular monthly schedule six years ago - showed Windows 7 was affected by nine of the 34 vulnerabilities, or 26% of the total.
Its count of critical bugs - the most serious as labelled by Microsoft - was five out of a possible 21, or 24%.
Windows Vista, meanwhile, was impacted by 19 of the 34 vulnerabilities - 56% of the total - with 11 pegged as critical.
Windows XP was affected by the most vulnerabilities of all: 24 out of 34, or 71% of the total. Of the two-dozen bugs that needed patching in Windows XP, 18 - or 86% of the total critical count - were tagged as critical.
The tallies indicated that, at least this month, Windows 7 was afflicted with about half as many vulnerabilities as Vista, and about a third as many as Windows XP. Its critical-bug count followed the same pattern.
The flaws that did affect Windows 7 were probably due to recycled code, said security experts: "The Windows 7 vulnerabilities are coming from its legacy code base," said Jason Miller, the security and data team manager for patch management vendor Shavlik Technologies.
In fact, none of the vulnerabilities patched last week were Windows 7-only flaws. Of the five security bulletins that affected the new operating system, all five also impacted Vista and XP, and all but one had to be patched in the even older Windows 2000.
The phenomenon of vulnerabilities in old code isn't new. Just months after Vista's launch, security researchers took Microsoft to task for overlooking a vulnerability in Windows' animated cursor in the brand-new operating system that was closely linked to a bug Microsoft had patched more than two years before.
Microsoft has promoted Windows 7 as safer and more secure than its predecessor, something it did two three years ago when it touted Vista as better than XP.
Even Microsoft's top expert on designing software with security in mind - a process Microsoft calls Security Development Lifecycle, or SDL - has admitted that it is virtually impossible to catch some kinds of bugs without tedious line-by-line review of the code, something even Microsoft is hard-pressed to do.
On the bright side for Microsoft, three of the five critical vulnerabilities assigned to Windows 7 are in Internet Explorer 8, the browser that ships with the new OS.
The remaining two are in older editions of the .Net Framework and Silverlight, the .Net-based cross-browser, cross-platform media standard that Microsoft is pushing.
Windows 7 was also unaffected by the eight vulnerabilities in GDI+ (Graphics Device Interface), which was put at the top of the to-patch list by most experts. Windows XP users had to apply six of the eight GDI+ fixes, while Vista users had to deploy just one.
That doesn't mean researchers and hackers won't uncover flaws in Windows 7 as time goes on.
"Unless Microsoft can make a brand-new operating system, bad things will continue to happen," said Miller of Shavlik.
Users already running Windows 7 can update now, but users who upgrade to Windows 7 starting this week will need to run Windows Update to obtain the patches after they have installed the new operating system.
Keep up with the latest news on Windows 7.