Data furnished by e-mail service provider MessageLabs placed the , which hit the Internet last August, at the top of its list of hostile attachments. MessageLabs intercepts such attachments for its clients.
Antivirus company Trend Micro's virus-tracking center placed SirCam at No. 3, right after and a variant of that 6-month-old worm.
The success of the old computer viruses is the result of continued susceptibility on the part of home computer users, said John Harrington, U.S. marketing director for U.K.-based MessageLabs.
"Most of those home users don't have antivirus programs in place, and when they do have them in place, they don't download the newest signatures," Harrington said.
While businesses tend to respond to the threat of a new virus within days or weeks,are not only more likely to leave a computer open to attack, they're also more likely to open a worm attached to an e-mail message.
Not all leading viruses were released last year. A third antivirus company, Russia-based Kaspersky Labs, released a Top 20 virus list for March, placing the , released on the Internet in mid-January, in the No. 1 position. SirCam reached the fourth-highest position on Kaspersky's list.
Which viruses top which lists varies depending on what the companies measure and the region in which a company's products are most popular, said MessageLabs' Harrington.
MessageLabs counts the number of attachments found in e-mail sent to its clients, so worms that send more e-mail will generally top its list.
Kaspersky and Trend Micro count the number of incidents reported to their support centers. Trend Micro also counts the number of computers scanned by its online antivirus scanner that were found to be infected. Kaspersky tends to be more popular in Europe and Russia, while Trend Micro is most popular in the Asia-Pacific region.