Microsoft's MSN Messenger service is back up and running after week-long interruptions left almost a third of its users disconnected or without access to their online personal address books.
About one per cent of its users will now have to rebuild their buddy lists for the free instant messaging (IM) service.
In a statement MSN vice president Richard Bray said: "We are pleased to announce that the interruptions to the MSN Messenger service have been resolved.
"All customers worldwide again have access to their MSN Messenger accounts and more than 99 per cent of all MSN Messenger customers have had their contact lists restored.
"Due to unforeseen circumstances in the final restoration of data, we were unable to restore contact lists for a small number of MSN Messenger customers."
The problems began on 3 July when almost 12 million users of the online messaging service were unable to pull up their contacts lists because of a hardware failure at Microsoft's Redmond headquarters.
Bray explained that it was necessary for the company to reboot and restore all MSN Messenger servers as part of its efforts to restore the service. "On a server, a disk controller failed and a backup controller had an error, which resulted in a more lengthy path to full service recovery," he said.
According to Microsoft, as users log back into the service, the software will automatically attempt to restore any of their contacts that are currently online and to add other contacts as they come online.
Nicole Lewis, an analyst at Jupiter Media Metrix, said the most serious ripple effect is "that there isn't a ton of loyalty among IM users. This is particularly true for MSN and Yahoo and a little less for AOL."
Yahoo reported a 25 per cent increase in downloads of its IM software during Microsoft's outage.
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