Denes Nemestothy from Network Integrity Services (NIS) warns that many firms have failed to upgrade their encryption security over the years and now risk having data stolen.
"This is a real problem and something that construction managers must look at immediately," he said.
"It’s not normally a problem for companies that have had a wireless network installed within the last 12 months or so by a reputable IT company.
"But if you had a wireless network put in a few years ago, the encryption on it may be out of date. And that means it is easier for a hacker to get into the network."
Denes explained that the problem isn’t just people "stealing" broadband from businesses, although that will slow the internet down for workers.
Some hackers can also access and copy data by monitoring all the traffic on the network and making a copy of it.
"Companies that are relying on old fashioned encryption called WEP are most at risk," Denes added.
"We recommend to all our clients that their wireless network is protected by the latest WPA2 security. This makes it significantly harder for hackers to get in. It’s the most up-to-date wireless security you can get."
NIS advises businesses across the UK how to keep their networks secure and working efficiently. The company deploys its Network Integrity Monitor to automatically check the status of all the components of a customer’s network, and this can also include carrying out full security audits of such important hardware as Wifi routers.
They also advise clients to use cloud computing – where applications and data are accessed via the web – to dramatically slash IT costs while improving business efficiencies.
The company was recently awarded Gold Certified Partner status by Microsoft, and has also been accredited as a business partner by IBM.