City law firms were left reeling after the LoveLetter virus hit London last Thursday.
The bug, which is thought to have started in the Philippines, struck businesses worldwide and even infiltrated the House of Commons.
Carried in an attachment to an email labelled "Iloveyou", the virus forwards itself to every email address on the computer, jamming computer servers and destroying picture files.
Clifford Chance, Denton Wilde Sapte and Herbert Smith all had to close down their computer systems, leaving lawyers relying on forms of communication they thought had died out.
A source at Clifford Chance says: "[The virus] has been contained now but it was a nuisance. Lawyers have been spending time re-acquainting themselves with pen and paper and telephones. There was no permanent damage."
One Denton Wilde Sapte partner says: "We were certainly hit terribly by it but I do not think we were hit any more than anyone else. We are still trying to clear it all up though."
A Herbert Smith spokes-man told The Lawyer that its systems are expected to be back to normal today (Monday).