Spyware - software that is downloaded by internet users without their knowledge and tracks their use of the web - is a bigger threat to dealer computer systems than traditional viruses.

Neville Briggs, managing director of DMS provider Pinewood's managing director, says: "About one in three PCs are infected with some form of spyware.

Usually, the software itself is just designed to report information for sales and marketing purposes to a third party. However, it does slow the PC down, causing screen 'freezes' and interrupting the normal running of software.

"What was new in 2004 is that spyware was previously only usually found if you visited some of the less mainstream corners of the internet, such as pornographic sites, so it didn't affect dealers to any great degree. Now spyware seems to be just about everywhere, and it is becoming a major problem for a lot of dealers."

During 2005, the problem is only expected to worsen, and Pinewood's advice to dealers is to buy anti-spyware software that monitors and removes spyware on each PC.