Microsoft is rushing to fix a bug in its widely used Internet Explorer web browser after a computer security firm disclosed the flaw over the weekend, saying hackers have already exploited it in attacks on some U.S. companies.
PCs running Windows XP will not receive any updates fixing that bug when they are released, however, because Microsoft stopped supporting the 13-year-old operating system earlier this month. Security firms estimate that between 15 and 25 percent of the world's PCs still run Windows XP.
Microsoft disclosed on Saturday its plans to fix the bug in an advisory to its customers posted on its security website, which it said is present in Internet Explorer versions 6 to 11. Those versions dominate desktop browsing, accounting for 55 percent of the PC browser market, according to tech research firm NetMarketShare.
Cybersecurity software maker FireEye said that a sophisticated group of hackers have been exploiting the bug in a campaign dubbed "Operation Clandestine Fox."