Two computer worms found last summer topped the charts in March, highlighting the difficulty of eliminating the more successful digital pests from the Internet.
Data furnished by e-mail service provider MessageLabs placed the SirCam virus, 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 centre placed SirCam at No. 3, right after Nimda 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, US marketing director for UK-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.