Microsoft on Thursday said that one-third of MSN Messenger customers were continuing to experience sporadic access problems and disappearing "buddy lists". However, the service appeared to go down completely around 3 pm PDT, with no users able to log in. Email sent to ZDNet from MSN members indicated intermittent outages that started Tuesday. Microsoft on Thursday attributed the difficulty to a hardware problem. "MSN has determined that up to approximately a third of MSN Messenger customers are unable to fully utilise the service due to a hardware failure that has affected the MSN Messenger service, including access to buddy lists," Sarah Lefko, Microsoft's MSN product manager, said earlier Thursday. "The majority of MSN Messenger customers worldwide are unaffected." Lefko said that while some people could still log in to the service, they would not be able to view their buddy lists. She emphasised, however, that those lists have not been lost. "When the issue is resolved, customers' personal buddy lists will be restored," she said. "There is no need for users to take any action to restore their personal buddy lists." Beginning Tuesday, many MSN Messenger users said they found their buddy lists of friends on the service had been wiped clean and that they could not keep constant connections to the service. The problem appears to be widespread, with MSN Messenger users in the United States, Korea, Singapore and Chile reporting failed connections or missing buddy lists. MSN Messenger uses Passport to log in to the service. Passport accounts are tied to an existing email address. Informal testing conducted by CNET News.com found that some Passport accounts using email addresses ending in non-Microsoft domains had lost their buddy lists. Some MSN Messenger accounts using Microsoft domains, such as msn.com, continued to function normally. Some Hotmail users, such as Kevin Benson, network/PC support manager for South Carolina Parks, Recreation, also reported problems and missing buddy lists. Benson said MSN Messenger would not retain new names added to the list. "When I add a user which requested to be added to my buddy lists, it added until I logged off and on again," he said. "The added user is now gone again." Daniel Darnell, an MSN Messenger user from Virginia, said he experienced login problems through Wednesday before signing back on to the service around 5 pm PDT. "But my entire buddy list was deleted, and I am supposed to have 14 buddies on my list," he said. "Before I went to bed I managed to add one of my buddies back, and this morning when I came on about (6 am) he was gone." MSN Messenger user Brad Taylor, from New York, said he "tried several times throughout the day" on Wednesday to connect to the service without success. He did, however, receive an email in response to a technical support request placed with Microsoft. "Recently, we encountered a technical problem that affected a small number of users on the specific system that contains your account; the problem affects the information that allows you to sign in to the MSN Messenger Service," the email states. "I apologise for this unusually lengthy period of downtime, and assure you that we are trying to restore sign-in availability as soon as possible." Throughout Thursday morning, people continued to report a string of seemingly unrelated glitches, including lost Hotmail address books and email and missing MSN Calendar information. But one common thread all these services share is Passport authentication. In fact, some people could not access their Passport accounts. Ray Bailey, information services manager for The Berquist Company, said that when he tried to log in, "I was told my Passport is bad, and I know that account is right." Passport is the cornerstone of Microsoft's ambitious HailStorm initiative. The company envisions a single login allowing customers access to a variety of services and information, all delivered to a wide range of disparate devices including PCs, handhelds and cell phones. Microsoft has been converting a number of its services over to Passport authentication. Late last month, for example, subscribers to the Microsoft Developer Network had to convert their logins to Passport accounts. "It will be interesting to see if Microsoft Passport can handle the load," said Guernsey Research analyst Chris LeTocq. The analyst also wondered if another expected load could be causing Microsoft problems. On Monday, the Redmond, Washington-based company issued the first preview release of Windows XP to about 100,000 people. Some of the features, including the new Windows Messenger, require Passport login. The glitch comes as the instant-messaging wars intensify on all fronts. AOL Time Warner claims more than 100 million instant-messaging users, compared with Microsoft's 32 million. Microsoft has responded to AOL Time Warner's closed-network approach by setting out to make its messaging product more attractive. The forthcoming Windows XP includes Windows Messenger -- a hybrid of instant messaging, videoconferencing, Internet telephone calling and application sharing. Some analysts say many of the features are attractive enough that Windows Messenger could help drive XP sales. See also: ZDNet UK's Windows News Section. Have your say instantly, and see what others have said. Click on the TalkBack button and go to the ZDNet news forums. Let the editors know what you think in the Mailroom. And read other letters.