Anti-virus firm Sophos has received a virus that infects Macromedia's Flash files, a feature that many sites use to entice casual visitors.
"It is more a proof of concept virus than one which poses a huge threat," says senior technology consultant for Sophos Graham Cluley.
The virus - known as SWF/LFM-926 - embeds itself into the script of Flash files and can infect all such files on a website.
Making movies
Flash animation has become popular as web designers create more and more snazzy sites with increasing amounts of interactive and multimedia features.
Many website creators have used the software to create games as well as animations and short films. Many websites allow visitors to bypass the animations on the opening pages of their site by providing a "skip intro" option.
Users could contract the virus by visiting a site and downloading an infected Flash file then running it in a separate Flash player.
Simply viewing a Flash film in a browser will not cause infection.
Sophos recommends that any site that uses Flash should ensure that its software is up to date and secure, to limit the chance that a pernicious file could be smuggled on to its server.
Live chat
E-mail worms, such as Nimda, that can multiply very quickly have caused havoc for many PC owners and have become a popular tool among many malicious hackers in recent years.
Throwing down the gauntlet with a clever new virus could be an ominous new development, warns Cluley.
"It is a new battleground and once someone has targeted a new area it is a challenge to other virus writers," he says.
Cluley predicts that Instant Messaging software - which is provided by firms like AOL and Yahoo and allows users to chat to their friends in real time - could become the next target of virus writers.
"People have learnt it is not a good idea to open attachments in e-mail but they are more comfortable about accepting files when they are chatting live to their friends," he says.