However, a wireless network that is not protected can provide a back door into a company's computer system, leaving sensitive material vulnerable.

A survey found 54% of Belfast firm's wireless networks were not encrypted.

Wireless or wi-fi networks have become hugely popular over the last few years in offices because they are easy to set up and make going online much more convenient.

About 2,000 networks across seven cities in the UK and Ireland were surveyed by computer firm Newell and Budge Security.

Managing director Conrad Simpson said would-be hackers could use basic equipment such as a standard laptop with a wireless network card to detect vulnerabilities.

"This was the second time we had done it, and Belfast certainly saw a marked improvement but it was still pretty damning in terms of the uptake of security," he said.

Out-of-the-box installations of these systems are too easy to do Graeme Pinkney Symantec

In Dublin, 71% of firms surveyed had unsecured systems while the average was 61%.

Graeme Pinkney of internet security company Symantec said it was an "ever growing" threat.

"Hacker communities will try to listen in to this information, so it's a push to try and keep up with the technology and enforce security," he said.

Mr Pinkney said educating businesses about the risks was the key to tackling the problem.

"Out-of-the-box installations of these systems are too easy to do," he said.

Mr Simpson and Mr Pinkney were speaking ahead of a conference in Belfast aimed at outlining the potential risks of wireless networks.

'Drive-by hacking'

Their findings mirror an international survey published earlier this month.

The survey of wi-fi networks in London, Frankfurt, New York and San Francisco by RSA Security found more than a third had basic security features turned off.

Many firms were simply turning on their wireless net access points and used default settings that anyone familiar with the technology could easily find out, the researchers found.