Research carried out by cfc solutions shows that fewer than half of fleets have both anti-virus software in place and a policy on e-mail and internet usage.
Many, it found, have no protection in place at all.
Managing director Jason Francis said: 'Many fleets have had to deal with the Mydoom virus recently. Very few organisations escaped it altogether.
'However, there is a huge difference between those fleets which have adequate virus protection in place and those that don't. The former will have solved the problem in a matter of hours, the latter may still not have found a solution.'
Mydoom is widely acknowledged to be the most virulent virus ever, infecting up to one in 12 of all e-mails sent recently.
Viruses can be spread as an e-mail attachment which, if opened, copies itself to other e-mail addresses. Cfc said it also potentially allowed unauthorised remote access to the infected machine.
Francis added: 'The problem exists at two levels. The first is that smaller fleets are usually part of smaller organisations that are less likely to have any form of virus protection in place or to ensure that it is kept updated.
'However, problems also exist in large businesses. While here the IT support is likely to be good and virus protection taken seriously, the sheer volume of e-mail and internet data that they deal with makes the risk of infection high. This is especially true as e-marketing to large fleets continues to increase.'
Francis added that while having anti-virus software in place was important, a strong corporate policy on e-mail and internet usage was also essential.
Corporate safety concerns boosts CFC business
HEALTH and safety concerns helped cfc solutions to a record year in 2003, the company said.
Managing director Jason Francis said: 'Health and safety has been the primary topic of conversation among our customers for the past year and many of them have recognised that fleet software is the ideal tool to help them meet their obligations.
'With the introduction of our specialist Corporate Liability Module at the end of 2003, we believe that we are ideally placed to enjoy an even better performance this year.'