The devastating damage that viruses can do to a network of PCs is well understood, and companies have long been protecting against the danger by implementing antivirus applications.

But the explosive and, in corporate terms, largely unmanaged growth of mobile computing threatens to undermine traditional virus protection.

The principal problem comes from the fact that PDAs and smartphones create backdoors into corporate infrastructures that can be exploited by viruses and malicious code to spread infections.

Rob Bamforth, practice leader at Bloor Research's Mobile and Wireless Practice, said that one of the principal security problems associated with mobile devices is that they are typically brought into organisations by individuals who have purchased them independently, rather than being issued as part of an co-ordinated IT department rollout.

This makes them very difficult to control and manage when they are connected to corporate networks.

Bamforth added that, while viruses currently present little danger to the actual mobile handsets themselves, the greatest problem comes from the devices being used as a transmission medium through which viruses could infect company infrastructures.

"There are two main issues with mobile viruses. The first is the danger of the devices itself being infected by a virus specific to its platforms," he said.

"But the other issue, which people tend to gloss over, is the biggest danger. This is the problem of what the mobile devices can upload onto the network.

"It's the danger of a PC virus being uploaded to a corporate network by the mobile device, rather than the device itself being directly attacked.

"This is an area that companies have yet to address properly. There are lots of tools around and there are lots of vendors with smart ideas and products that can address the problems.

"But at the end of the day policy and procedures are what security stands or falls on. The rest of it is just tools, which are useless unless they are implemented properly."

Jack Clark, a member of the AntiVirus Emergency Response Team at security company Network Associates, warned that the danger from mobile viruses, while insignificant at present, is set to grow dramatically as the use of PDAs and smartphones proliferates.

"Where there is new technology, there will be people trying to exploit its weaknesses as well as its strengths," he explained.

"As convergence becomes a reality, and mobile devices are able to house more and more sensitive information, the threat of malicious mobile virus code increases.

"One thing is for certain though: mobile devices and operating systems are firmly on the agenda of virus writers all around the world who relish the challenge of entering the mobile market.

"In order to predict the future we need to look as the past. How many organisations realised the importance of antivirus software after being hit by Melissa?"

Clive Longbottom, strategy analyst at research firm Quocirca, agreed that companies need to be aware of the growing threat from mobile viruses and implement countermeasures.

"There have already been viruses identified that target mobile handsets and there will be a hell of a lot more as smartphones start to take off. For PDAs there have been Palm viruses and also infections on the Microsoft Pocket PC platform," he said.

"As we become more mobile companies are slowly waking up to the threat and are starting to look for antivirus protection for mobiles.

"There are a number of antivirus vendors that have already developed products that protect against this type of threat, but they are not promoting them at the moment as there is little demand."

This view is endorsed by Raimund Genes, president of European operations at antivirus company Trend Micro. He said that there is currently little problem with mobile devices spreading malicious code into enterprise networks because most PDAs and phones have relatively simple operating systems.

But Genes warned that this is changing as the operating systems become more sophisticated, and always-on connections such as GPRS become more common.

"At the moment the operating system in mobile devices is limited and fairly well shielded," he explained. "But there will be more and more demand from the customers for applications. I believe that by 2005 we will have a real problem with viruses on these phones."

According to the 2002 Corporate Wireless Survey conducted by analyst company Yankee Group, security concerns are creating a serious barrier to mobile data adoption for the majority of enterprises.

Eugene Signorini, senior analyst at the Yankee Group, stated: "Sixty-eight per cent of respondents 'somewhat' or 'strongly' agree that security is a barrier to the adoption of wireless data services, reflecting an overall concern within enterprises surrounding security for all information technologies.

"With fixed networks continuing to succumb to security breaches, there is a perception that wireless networks are even more vulnerable to unauthorised access."

Mike Short, chairman of industry body the Mobile Data Association, advised companies to select a professional partner to develop their mobile security and antivirus policies.

"The first challenge is to find the right partner," he said. "When you go from a wired to a wireless local area network you must have specialist help. Most enterprises don't really have the technology depth in-house to achieve this difficult transition."