"The Internet's Domain Name System (DNS) did not return the correct response when it was queried for a Microsoft Web site," said Ruud de Jonge, support manager at Microsoft Benelux.
The first reports of the problem started coming in "very early" Wednesday morning, said De Jonge.
Microsoft has yet to pin down the cause of the DNS error. "It can be a system or human error, but somebody could also have done this intentionally," De Jonge said. "We don't manage the DNS ourselves, it is a system controlled by the Internet Corporation for Assigned Names and Numbers (ICANN) with worldwide replicas."
Because of the blackout, some 60 million Hotmail users worldwide were unable to access their e-mail, Microsoft customers could not download software updates or get online support and MSNBC.com had no audience. Services which at 10.20am AEST could not be reached included Windowsupdate.com, which contains updates for the Windows operating system and bCentral.com, a portal for small and medium sized businesses.
Hackers could be responsible for the outage said Simon Hania, spokesman for Dutch Internet service provider XS4ALL Internet BV. "The name server that is authoritative for Microsoft's Web sites might have crippled under a Denial of Service attack," he said.
Hania said, however, it is more likely that a network error or system failure caused the problem.
The DNS consists of many machines around the world set up in a hierarchy. "It looks like the machine hit is in the top of the DNS tree," Hania said. "Once it is fixed it can take a couple of hours for all DNS systems around the world to pick up the correct DNS information."