One of the four will impact all instances of IE, so there's a very high chance that that update would have patched the pertinent editions of the browser -- IE6, IE7 and IE8 -- on Windows XP if Microsoft had continued updating the old OS. The upcoming fix for IE was rated "critical," Microsoft's highest threat warning, and was also tagged with the phrase "remote code execution" in last week's advance notification, meaning that if successfully exploited, attackers could hijack the PC and plant malware on its drive.
Two of the remaining three updates also strongly hint at XP vulnerabilities, albeit less threatening ones, since they will apply not only to the newer client editions, like Windows 7 and 8, but also to the still-supported Windows Server 2003, which has a considerable amount of code in common with XP.
The only good news, said Secunia last week, was that Windows XP's retirement triggered a sharp decline in its share of U.S. PC operating systems. In the three weeks after April 8, XP's share dropped nearly 17 percent, said the Danish security company.
The decline of one percentage point each week took Windows XP from an 18 percent share before retirement to 15 percent for the week April 23-29. The three-point drop represented one-sixth, or 16.7 percent, of the original 18 percent share.
Secunia measured operating system share by tallying the machines that accessed its patch management tools, including the free Personal Software Inspector (PSI), a utility that identifies out-of-date Windows applications and add-ons, then delivers security updates.
Other measurements of Windows XP, including a global estimate by Net Applications earlier this month, pegged Windows XP's presence considerably higher, mostly because huge numbers of Chinese computers still run the OS. Net Applications reported that XP powered about 26 percent of all desktop and notebook personal computers in April.
StatCounter, an Irish analytics company, said that XP's share in the U.S. averaged 13 percent last month, a drop from 15 percent the month prior.
Secunia's numbers imply that the demise of patch support for Windows XP has prompted a significant portion of American die-hards to finally discard the operating system, presumably replacing it with Windows 7, 8 or 8.1, or in some instances, with a Mac or another type of computing device, such as a tablet.
Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer, on Google+ or subscribe to Gregg's RSS feed. His email address is firstname.lastname@example.org.
Read more about malware and vulnerabilities in Computerworld's Malware and Vulnerabilities Topic Center.