A denial-of-service attack rendered Microsoft's corporate Web site inaccessible for more than an hour on Friday afternoon, amid heightened fears that a major Internet attack could be on the horizon. Microsoft's Web site became largely inaccessible at about 12:50 p.m. PST, according to reader reports received by CNET News.com. The site appeared to be back up and running around 2:15 p.m. The outage occurred as system administrators and security experts were bracing for a potentially large Internet attack. The U.S. federal government warned earlier this week that an attack could be brewing that exploits a widespread flaw in Microsoft's Windows operating system.

Microsoft spokesman Sean Sundwall said Microsoft was the victim of a denial-of-service attack, but he stressed that no Windows vulnerability was exploited. "We're investigating the cause of the issue," Sundwall said. "One thing we do know is it is not an issue associated with any vulnerabilities. It was a very traditional denial-of-service" attack. The software maker announced a patch for the flaw two weeks ago. However, the outage temporarily prevented some customers from reaching Microsoft's security patches.