The research found that 84% of firms know the data storage devices are being used by staff, but few are policing what people are putting on them.

Almost one-third of organisations say users are connecting up the devices to PCs without permission.

As the removable drives get cheaper and can store more data, firms risk losing huge amounts of sensitive information.

Drive-by infection

Many companies are spending huge sums of money to protect their employees from viruses, spyware and spam but they could be ignoring another danger, warns a survey from PointSec.

The security firm found that the increasing popularity of media players like the Apple iPod and greater use of tiny USB drives, that many people carry on a keychain, is exposing many firms to real security risks.

In its survey of technology staff, PointSec found that the vast majority of firms knew that portable drives were being used by staff.

Almost a third of the staff within these firms were thought to be carrying round portable media players or USB flash drives.

Few firms were doing anything to stop files being downloaded on to media players or drives. The fact that many media players can store gigabytes of data means they could potentially store huge amounts of sensitive information.

Although the problem of people downloading confidential information and walking out of the door with it is not new, said Martin Allen, UK managing director of PointSec, the greater capacity of current drives is making the problem potentially much worse.

Moving files from home to work could expose firms to risk from viruses and other malicious programs.

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Mr Allen said a ban on the use of portable players and USB drives in the workplace would not work. Instead firms needed to do a better job of monitoring what was being placed on drives.