"Critical" security problems with Microsoft's Windows software could let hackers break into computers to steal files, delete data or eavesdrop on sensitive information.
The US software giant, which learned about the flaws more than six months ago, says the only protection is a repair patch available on its website.
It assessed the threat to computer users as "critical" - its highest rating.
A Microsoft security executive, Stephen Toulouse, said the flawed software was "an extremely deep and pervasive technology in Windows".
He urged customers to apply the patch immediately.
The US Department of Homeland Security also warned about the software problems with e-mails sent across its new national cyber-alert system.
The news comes just weeks before Microsoft Chairman Bill Gates delivers a keynote speech in San Francisco at a leading security trade conference.
Microsoft has struggled in recent months against a tide of renewed criticism about security risks in its software, the engine for computers in most of the world's governments, corporations and homes.
Microsoft has urged consumers to apply the repairing patch immediately if they are have windows NT, Windows 2000, windows XP, Windows NT Server, Server 2000 and Server 2003.
The US software giant, which learned about the flaws more than six months ago, says the only protection is a repair patch available on its website.
It assessed the threat to computer users as "critical" - its highest rating.
A Microsoft security executive, Stephen Toulouse, said the flawed software was "an extremely deep and pervasive technology in Windows".
He urged customers to apply the patch immediately.
The US Department of Homeland Security also warned about the software problems with e-mails sent across its new national cyber-alert system.
The news comes just weeks before Microsoft Chairman Bill Gates delivers a keynote speech in San Francisco at a leading security trade conference.
Microsoft has struggled in recent months against a tide of renewed criticism about security risks in its software, the engine for computers in most of the world's governments, corporations and homes.
Microsoft has urged consumers to apply the repairing patch immediately if they are have windows NT, Windows 2000, windows XP, Windows NT Server, Server 2000 and Server 2003.
