Security researchers on Tuesday detected hackers distributing software to break into computers using flaws announced last week in some versions of Microsoft Corp.'s Windows operating system.

The threat from this new vulnerability -- which already has drawn stern warnings from the Homeland Security Department -- is remarkably similar to one that allowed the Blaster virus to infect hundreds of thousands of computers last month.

The discovery gives fresh impetus for tens of millions of Windows users -- inside corporations and in their homes -- to immediately apply a free repairing patch from Microsoft. Homeland Security officials have warned that attacks could result in a "significant impact" on the operation of the Internet.

Researchers from iDefense Inc. of Reston, Va., who found the new attack software being distributed from a Chinese Web site, said it was already being used to break into vulnerable computers and implant eavesdropping programs. They said they expect widespread attacks similar to the Blaster infection within days.

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