Users of Microsoft's MSN Messenger service have encountered access problems and had buddies mysteriously disappear from their lists over the last few days.
The company said that approximately one third of its 32 million users might have been unable to access all features of the service.
Reader emails sent to vnunet.com suggest that a server crash was responsible for the outage and users all around the world were affected.
Since Wednesday users have encountered problems logging in to the service and experienced difficulties with their buddy lists as contacts disappear, seemingly at random.
Rumours instantly began circulating that Microsoft's single-sign-on Passport service was to blame, but according to reports from the company, the fault lies in a hardware failure.
The company was also quick to dispel any myths that user data had been lost.
Microsoft said that all buddy lists would be fully reinstated as soon as the glitch is fixed, but it is still unclear whether the problem has been found today.
This isn't the first hiccup encountered by Microsoft this week. When the company released Windows XP Release Candidate 1 on Tuesday, a link appeared on user news site Maxreboot.com allowing users to download the release directly from Microsoft itself, without needing any form of login or password.
It is believed that thousands of users hit the connection to get the file, which is rapidly spreading across the underground warez scene.
Microsoft has since fixed this problem.
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