A new version of the Sobig.F e-mail virus that has plagued computers worldwide could arrive any day and before the latest variant is timed to expire on September 10th, security experts said.
Mr Mikko Hypponen, manager of anti-virus research at Finland-based F-Secure Corp, said one of the five prior versions of Sobig surfaced before the previous version expired. Sobig.E began circulating June 25th, one week before Sobig.D was set to expire, he said.
The first version of Sobig arrived in January and had no expiration date. It was followed about four months later by Sobig.B. More sophisticated versions followed one week to three weeks after each preceding version.
The latest version, Sobig.F, first emerged a week ago and spread to hundreds of thousands of Windows-based computers. Some 200 million e-mails have been sent over the Internet by infected computers.
Sobig.F spreads when unsuspecting computer users open file attachments in e-mails with headings like "Thank You!," and "Re: Details." Once the file is opened, Sobig.F resends itself to e-mail addresses from the infected computer, using random names as the sender.
Sobig.F was programmed to send infected e-mails to one of 20 master computers to receive more instructions on Friday and Sunday, but both attacks failed when the 20 computers were taken off line by computer security specialists.
Infections have declined since last week, falling to a little under 100,000 affected computers by yesterday.