Microsoft this week will stop issuing security fixes for computers running the Windows XP operating system updated with Service Pack 2.
The switch-off will result in hundreds of millions of PCs worldwide, including tens of millions in the U.S., instantly becoming riper targets for hackers.
So-called XP SP2 desktops and laptops are still widely used in corporate networks. A service pack is a collection of feature upgrades and security fixes delivered in a single download.
Microsoft released SP2 in August 2004 mainly to beef up security. Then in April 2008, the company released SP3 with less fanfare, recommending that all XP computers be updated with the latest service pack. Yet more than two years later, thousands of companies worldwide have not done so.