The flawed software update was included in the firm's Wednesday LiveUpdate.
"America Online is your internet service provider. You ran LiveUpdate on March 15, 2006, and now you cannot connect to AOL," Symantec said on its website. "A Symantec intrusion-detection signature that was included in the March 15 LiveUpdate caused this problem. Symantec has updated the signature to fix this problem."
The company recommended that Norton Internet Security users temporarily disable security features until they download new updates.
Earlier this week, McAfee had misdiagnosed a number of files using an incorrect identification file called 4715 DAT. The error could have resulted in users incorrectly deleting files.
The SANS Internet Storm Center had earlier this week recapped the woes of one system administrator forced to restore 3,700 quarantined files.