After all the scare stories about MI5 officers leaving their laptops in pubs it seems that people are still unable to look after their mobile computers.

A survey of 500 information security professionals conducted by the Ponemon Institute found that more than 80 per cent of firms have put critical data at risk by losing a laptop containing sensitive information in the past 12 months. 

The US Department of Transportation has lost two laptops in Florida recently, one stolen from a conference room in Orlando on 24 April and the second half-inched in July from a government vehicle in Miami.

The latter contained the names, addresses, birthdates and social security numbers of some 133,000 Florida residents.

According to security experts, laptops and PDAs are stolen to order by cyber-criminals because they offer one of the easiest ways to bypass company security and access sensitive data.

Ponemon's report suggested that the problem is companies not knowing where critical data resides.

Some 64 per cent of respondents had never conducted an audit of sensitive data, so it leaks out on laptops, mobiles and USB data sticks without anyone knowing.

The Ponemon phenomenon has been known to security consultants for some time. "Too many IT managers still think that the essence of security is to harden the perimeter of their network against internet hacks and worms," said one security specialist.

"But that is so 1999 and all it does is protect bits of the physical infrastructure while critical data is whizzing around unprotected on laptops and email-enabled mobiles outside the perimeter fence."

The increasingly mobile nature of business means that data has to be protected wherever it resides. For mobile devices, that means using encryption.