Cyber security 2Lt William Liggett works at the Air Force Space Command Network Operations & Security Center at Peterson Air Force Base in Colorado Springs, Colorado. REUTERS/Rick Wilking

Cyber crime is a growing problem for all businesses.

But it's not just about people on computers in remote locations trying to find a crack a firewall, there's a physical element too.

Attaching a device via USB to a company computer can increase the effectiveness of a cyber attack - it's just a case of getting into the office to do it.

According to Peter Connolly, chief executive of Toro Risk Solutions, a gang can bribe a cleaner to do just that for as little as £80 ($116).

In 2013, Barclays lost £1.3 million ($1.8 million) in a hacking attack after an insider fitted a device that allowed a gang to access accounts.

Experienced criminals are often able to just talk their way in. Toro tests how vulnerable a company is to social engineering - in other words, how easy it is for someone to gain physical access to corporate servers or computers by pretending to be someone else.

"It's real Derren Brown stuff," Connolly said.

He added that professional gangs of cyber criminals can encrypt a company's data for a certain period of time, demanding a ransom from the company with threats to wipe information on customers and erasing weeks or months of work.

Ransoms are often demanded in Bitcoin, the digital cryptocurrency, Connolly said.

Gangs have found that their victims are so confused by the demands that many have set up English-language telephone hotlines that help them convert their pounds and dollars into Bitcoin and pay the ransom.