Portable media players like the iPod pose a significant security risk according to figures from software auditors Centennial Software.

Nearly nine out of ten of the 220 IT managers questioned took no action to prevent such devices coming into the workplace even though over half of them recognised storage devices like the iPod as a threat.

"External security risks are well documented, but firms must now consider internal threats, which are potentially even more damaging," said Andy Burton, chief executive of Centennial Software.

"Deliberate or accidental, the damage caused by the misuse of removable media devices can be disastrous. Employees can seriously endanger the company by taking sensitive information off-site, introducing viruses, or simply creating a build up of unwanted files on the network."

The survey found that many IT managers were ignoring the issue, with over a third saying they did not view the devices as a threat.

Portable devices like the iPod can be used to store a whole variety of data, including documents and spreadsheets. The average word-processing file is between 25k and 30k, meaning that a 20GB player could hold more than 750,000 documents.