Microsoft Corp 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 get any updates fixing that bug when they are released, however, because Microsoft stopped supporting the 13-year-old operating system this month. Security firms estimate 15 percent to 25 percent of the world's PCs still run Windows XP.
Cybersecurity software maker FireEye Inc. said a sophisticated group of hackers has been exploiting the bug in a campaign dubbed "Operation Clandestine Fox." FireEye declined to name specific victims or identify the group of hackers, saying an investigation is still active.
Microsoft said the vulnerability could let a hacker take complete control of an affected system.