Microsoft blames DNS configuration error in blackout


Microsoft Corp. said late Wednesday that it was to blame for a fault that resulted in many of its web sites being inaccessible to millions of Internet users.

"At 6:30 last night, a configuration change was made by a Microsoft technician to the routers on the edge of Microsoft's DNS network," the company said in a statement. "The mistaken configuration change limited communication between DNS servers on the Internet and Microsoft's DNS servers. This limited communication caused many of Microsoft's sites to be unreachable, although they were actually still operational, to a large number of customers throughout last night and today."

DNS servers are responsible for translating addresses, such as or, into the numeric IP (Internet Protocol) addresses that computers use to communicate with each other. When the DNS system is not available or corrupted, software in a user's computer is unable to find out the numeric address and so is unable to communicate with the desired server.

"This was an operational error, and not the result of any issue with Microsoft or third-party products nor the security of our networks. Microsoft regrets any inconvenience caused to customers due to this issue," the company added.

Microsoft said the fault was rectified at 5 p.m. PST when the original changes were removed -- some 22 1/2 hours after they were originally uploaded. The company, "immediately saw a massive improvement in the DNS network," when the settings were restored, it said.

The problems hit a number of the Internet's most popular sites including the company's main site, web based e-mail site, web portal, news site, travel and vacation site, online car sales and information service and the reference site.

As the business day progressed, users in parts of the U.S. gained access gradually to some of the software giant's Web sites. Some users on the East coast reported no problems accessing any of Microsoft's sites this afternoon, while others in Chicago, Austin, Texas and San Francisco reported difficulties.

"By mid-afternoon, I could get to Hotmail, MSN, and Expedia, but still had no luck with," said Arturo Castellanos, a system administrator at Austin-based online travel company GeoPassage Corp. A user in London also said she was able to reach the email and travel services but not Microsoft's home page and most users in San Francisco were blocked from accessing any of Microsoft's properties late into Wednesday afternoon.

The problems also proved frustrating for the nearly 60 million Hotmail subscribers around the world, many of whom were cut off from their email.

IDG News Service reporter Ashlee Vance coauthored this article.

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