America Online, MySpace.com and Earthlink all had problems with user log ins, and with access to home page or archived e-mail accounts.
While the heavily used services often experience temporary outages, the simultaneous nature of the current problem raised eyebrows at several security companies and response teams, though none had confirmed any malicious attacks by early afternoon Eastern time.
A Symantec spokeswoman said one backdoor worm threat to MSN Messenger had been reported earlier on Friday, but the threat did not seem broad enough to cause widespread problems. AOL brought its log-in service back up by noon Eastern, though MySpace and Earthlink were continuing to experience problems by early afternoon.