The latest variant of the Sober worm, called the most widespread virus outbreak ever, has infected one in every 13 email messages, according to a leading online security company.
Over a seven-day period last month, 218 million Sober-infected messages were quarantined by Postini - more than twice as many as the previous largest attack on record.
The company said it also intercepted 29 million copies of the virus in a 24-hour span.
"We typically quarantine about 50 million virus-infected emails in a month. This Sober virus generated close to a 1,500-percent increase in virus-infected email traffic in the past week," said Scott Petry, Postini founder and vice president of products and engineering.
The latest variant arrives as a .zip file email attachment in either German or English that a user must be tricked into opening. Recently, Sober has passed itself off as a warning from the FBI, CIA or German law enforcement, as well as videos starring "The Simple Life" television stars Paris Hilton and Nicole Ritchie.
Once downloaded, the virus harvests email addresses from a PC and replicates itself as spam to new recipients.
Sophos has reported that the virus recently accounted for 88 percent of all viruses reported to the company, confirming its status as the most widespread virus on record.
Graham Cluley, senior technology consultant at Sophos, said the volume "should be a wake-up call to businesses across the globe as to the major level of threat that viruses pose to IT security."
"The sheer rate at which this worm is spreading proves that the devious tricks used by the worm's creator are working," he said.
The U.S. Computer Emergency Readiness Team has warned that the virus may terminate running processes or "open a backdoor on the system that allows the attacker to communicate remotely with the system via IRC.
