Later he wrote about how things seemed. "When I have been connected to other person's data, my icon and computer name show on the screen for a microsecond, and then they are replaced with the other person's icon(s) and computer name(s). This must be a glitch in their link between their logon and authentication module and the link to the actual storage files which belong to each particular user."

Howland said he decided to immediately stop using Norton Online backup.

Howland added that a Norton Online Backup technician remotely assisting him in resolving the problems he was experiencing saw the display of the files from another user, but didn't comment on it at the time. Howland indicated he provided Symantec with evidence of the data breach. It turned out Howland had indeed identified a problem.

Symantec acknowledges it began investigating these questions on Aug. 7 and "fixed the issue within 24 hours by rolling the server software back to an earlier state," though the security vendor isn't saying how many Norton Online Backup customers were impacted. "As of August 8, no further instances of this error have occurred."

Ellen Messmer is senior editor at Network World, an IDG publication and website, where she covers news and technology trends related to information security. Twitter: @MessmerE. Email: emessmer@nww.com.