Users of Microsoft's MSN Messenger program on Thursday said access to the service has been sporadic for more than a day. Email sent to CNET News.com from MSN members indicates that a sporadic outage is under way that could be linked to Microsoft's Passport authentication system. Starting Tuesday night, many MSN Messenger users found that their "buddy lists" of friends on the MSN Messenger service had been wiped clean and that they could not keep constant connections to the service over the 4 July holiday. The problem appears to be widespread, with MSN Messenger users in the United States and as far away as 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. Other 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 buddies 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, a MSN Messenger user from Virginia, said he experienced login problems through Wednesday before signing back on to the service around 5pm 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 (6am PDT) 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 e-mail states. "I apologize for this unusually lengthy period of downtime, and assure you that we are trying to restore sign-in availability as soon as possible." Microsoft could not immediately be reached for comment. As of 6.45am PDT, the company had yet to post a technical-support document about the situation. Is your PC safe? Find out in ZDNet UK's Viruses and Hacking News Section. Have your say instantly, and see what others have said. Click on the TalkBack button and go to the Security forum. Let the editors know what you think in the Mailroom. And read other letters.