In order to prevent the network from viruses and hacker attacks, most companies insist their computers are "locked down" so that employees can’t run unauthorised software or CD and DVD content.

But the same rule doesn’t apply to the senior leaders of a company.

"But woe betide the lowly IT director that would inconvenience the CEO with such restrictions," New Scientist magazine quoted Glenn Zimmerman, a technology expert with the Pentagon’s cyberspace task force, as saying.

Warning a London conference on Cyber Warfare, he said that “most senior leaders'' computers are often wide open to threats," and that it was often the CEO who held the most critical data.

Cyberwar analyst Yael Shahar of the International Institute for Counter-Terrorism in Herzliya, Israel, suggested that the best way to deal with this threat from within is to hack their computers and show them what you find.

"They may close the door and show you out, but their security awareness will have gone up a notch," she said.

Zimmerman said that the solution would be to use less arduous security measures.

He pointed out that locking down PCs made tech-savvy users to find workarounds, which introduce vulnerabilities.