As explained here, the worm's actions include changing registry keys and adding links to various Web sites (e.g. Nude Nurses.url) to a victim's favourites list.
Although the virus is relatively uncommon, the fact that it is spreading at all is causing concern in security circles.
"We're getting some reports of infection by Fortnight but it's not particularly widespread. We're alerting people about Fortnight because it focuses attention of the failure of some people to apply security patches," said Graham Cluley, senior technology consultant for Sophos Anti-Virus.
"There really is no excuse for failing to apply a patch which has been around for three years.”