Enterprises are being urged to wake up to the growing security risks associated with employees installing Wi-Fi in the workplace without the permission or knowledge of IT departments.

"Deploy Wi-Fi or your employees will do it for you," warned Chris Clark, chief executive for wireless broadband at BT.

"The reality is that the benefits of Wi-Fi are very nice. As soon as individuals find this out they will install it themselves, if the IT department won't, and that's a huge security problem."

This has happened already at a large Boston financial institution, according to Anurag Lal, vice president of business development at wireless networking firm iPass.

Lal explained that the organisation had been in contact with iPass about introducing Wi-Fi in its offices. It decided not to install the network but called back six months later after discovering that employees had taken matters into their own hands.

"A simple sweep found 28 wireless access points on one floor alone," he said. "If Wi-Fi networks are not properly locked down they leave a huge hole in the security of the network as a whole. You have to move with the technology."

Lal also warned that until two years ago students attempted the majority of Wi-Fi hacking as an act of bravado.

But since then attacks increasingly focus on extracting monetary value from their targets, either directly or by identity theft.

The problem mirrors one from the early days of the internet. In the 1990s companies suffered attacks after employees attached modems to their phone plugs in order to access the internet.