A Microsoft official acknowledged that the risk to consumers was unprecedented because the glitches allow hackers to seize control of all Windows XP operating system software without requiring a computer user to do anything except connect to the Internet.
Microsoft made available on its Web site a free fix for both home and professional editions of Windows XP and forcefully urged consumers to install it immediately.
The flaws, discovered five weeks ago by independent security researchers, threatened to undermine widespread adoption of Microsoft's latest Windows software, which many hope will be an economic catalyst for the sagging technology industry.
The company sold more than 7 million copies of Windows XP in the two weeks after it hit stores Oct. 25.
The Windows XP problems affect a little-used feature that eventually will allow consumers to control high-tech household appliances using their computers. Called "universal plug and play," the feature is activated by design in every copy of Windows XP and can be added manually to Microsoft's earlier Windows ME software, also used by millions of consumers worldwide.
"This is the first network-based, remote compromise that I'm aware of for Windows desktop systems," said Scott Culp, manager of Microsoft's security response center. "Every Windows XP user needs to immediately take action." He called it a "verserious vulnerability."
Microsoft said a new feature of Windows XP, known as "drizzle," can automatically download the free fix, which takes several minutes to download, and prompt consumers to install it. Microsoft also is working with other software companies, such as leading antivirus and firewall vendors, to build protection into their products.
Maiffret and his researchers demonstrated the flaws for The Associated Press by hacking into a reporter's laptop running Windows XP from 2,300 miles away and successfully instructing the computer to connect automatically several times to the Web site for the National Security Agency, the government's super-secret spy agency.
Microsoft and Maiffret said there was no suggestion that anyone has used these flaws to break into any computers; Maiffret predicted that many hackers will be able to duplicate his firm's research and begin breaking into unprotected computers "a couple months from now."
Microsoft feared that hackers could exploit the flaws more quickly if eEye discloses too many details about its findings. Leading up to the public announcement, Culp said, those researchers behaved "exactly right" by quietly notifying Microsoft.
Riley Hassell, eEye's self-described "network penetration specialist," discovered methods for hackers to either disrupt a victim's Windows XP computer, order it to attack other Internet users or instruct it to run commands such as to delete or steal files or install rogue software.
"This is very serious," said Maiffret. Hackers using these methods "could reformat your hard-drive, record your keystrokes," he added.
Hackers could attack individual computers directly, though the flaws also allow hackers to transmit an attack to a single Internet address and strike all the nearby Windows XP computers within a corporation or neighborhood. Microsoft said companies and Internet providers can reduce the threat by properly configuring their Internet traffic-directing devices, called routers.
The flaws are particularly embarrassing to Microsoft because their discovery falls so close to Christmas and because of the company's commercial emphasis on improved security in Windows XP. The company boasts as one of 10 reasons for technology experts to buy Windows XP the promise of a "safe, secure and private computing experience."
"This is the most secure version of Windows we have ever released," said Culp, adding that complex software "will always fall short of perfection."
One of the problems disclosed Thursday belongs to a category of software flaws known as "buffer overflows," which can trick software into accepting dangerous commands. Another is the result of broader design problems with universal plug and play technology.
Just last week, Microsoft's corporate security officer, Howard Schmidt, expressed frustration about continuing threats from overflows. "I'm still amazed that we allow these things to occur," he said at a conferene of technology executives. Schmidt is expected soon to resign from Microsoft to work for President Bush's top computer security adviser.
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