Another critical flaw has been identified in Microsoft Windows, that could lead to major Internet attacks.

MICROSOFT HAS ACKNOWLEDGED the problem and has been offering a free fix on its Web site for the past two weeks.

But now the Department of Homeland Security warns that hackers have successfully tested new tools that allow them to seize control of vulnerable computers — stealing data, deleting files and intercepting e-mails. The agency says it’s also detected an Internet-wide jump in scanning for computers to victimize. (MSNBC is a Microsoft-NBC joint venture.)

Downloading the fix is easy for individual users, but large firms with thousands of computers need to change each one individually. Federal officials fear a “worm” would let hackers seize control of thousands of computers within minutes.

UPDATE: the patch is available here.

UPDATE: actually, the patch mentioned in the article is this one. There are so many Windows patches, it’s hard to get them straight.