The hack attack began Thursday morning and targeted the routers that direct traffic to the company's Web sites, Microsoft said in a statement. Access to some of the company's most popular online destinations, including the Microsoft.com home page and MSN.com Web portal, were intermittent for many customers throughout the morning, Microsoft said.
The software maker said it took steps to counter the attacks and that its Web sites were operating normally by Thursday afternoon. The company also said it has been in touch with the US Federal Bureau of Investigation (FBI) about the attacks.
DoS attacks disable a computer by bombarding it with a high volume of information requests in a short period of time, causing it to crash or become so overwhelmed that it grinds to a halt. A series of high-profile DoS attacks in February last year brought prominent Web sites, including Yahoo, Amazon.com and eBay temporarily to their knees, costing millions of dollars and raising new concerns about security on the Internet. Thursday's incident comes just hours after Microsoft's Web sites were knocked off line for almost a whole day by what the company said was a technical error made by one of its engineers Tuesday evening. In that outage, a technician working on the company's DNS (domain name system) network changed the configuration on one of its routers, blocking access to its sites, Microsoft said. Microsoft said the latest incident was "completely separate" from the outage that started Tuesday. One security expert was sceptical, however, saying Microsoft's problems may have been the result of a DoS attack all along.
"It is hard to believe that one problem is different from the other,"said Ric Steinberger, technical director at online security company SecurityPortal. "It is not always obvious from the start that something is DoS or due to a change in configuration. I think probably when the dust settles Microsoft is going to say this is all the result of a DoS attack."
DNS servers translate addresses, such as www.microsoft.com, into the numeric IP (Internet Protocol) addresses that computers use to communicate with each other. When a DNS system fails, Web browsers can't locate the IP addresses assigned to Web servers and hence can't open the desired Web page.
Microsoft said the type of attack it suffered Thursday was not related to any of its products, and apologised for the inconvenience caused to its customers. The outages also affected Microsoft's Hotmail free email service, which is used by millions around the world, as well as its Expedia.com travel site, MSNBC.com news site and auto sales site CarPoint.com. Corporate customers who use Microsoft's Web sites for technical help and to download software upgrades and security patches also found themselves locked out.
The steps taken Thursday should improve the company's protection against future DoS attacks, Microsoft said. The company will take additional steps in the weeks ahead to protect itself further against interruptions.
"It is unfortunate that an individual or group of individuals would engage in this kind of illegal activity," Microsoft said in the statement.