Internet Explorer users, please update now!

Microsoft on Saturday confirmed that Internet Explorer (IE) 6, 7 and 8 contain an unpatched bug -- or "zero-day" vulnerability -- that is being used by attackers to hijack victims' Windows computers.

The company is "working around the clock" on a patch, its engineers said. They have also released a preliminary workaround that will protect affected IE customers until the update is ready.

In a security advisory issued Dec. 29, Microsoft acknowledged that attacks are taking place. "Microsoft is aware of targeted attacks that attempt to exploit this vulnerability through Internet Explorer 8," the alert stated.

Newer versions of IE, including 2011's IE9 and this year's IE10, are not affected, Microsoft said. It urged those able to upgrade to do so.