Richard Stallman, founder of the Free Software Foundation, has warned that cloud computing is mainly "hype" and companies risk losing control of their data if they buy into such systems.

Stallman told The Guardian that cloud computing posed a serious danger, as businesses and individuals would lose direct control over their data by handing it over to third parties.

"It's stupidity. It's worse than stupidity. It's a marketing hype campaign," he said.

"Somebody is saying that this is inevitable, and whenever you hear somebody saying that, it's very likely to be a set of businesses campaigning to make it true."

Stallman added that computer users should keep their personal data on their own computers where it is secure, rather than trusting it to third parties.

He said that by storing data in the cloud users would become "putty in the hands of whoever developed that software".

"One reason you should not use web applications to do your computing is that you lose control," he explained.

"It's just as bad as using a proprietary program. Do your own computing on your own computer with your copy of a freedom-respecting program. If you use a proprietary program, or somebody else's web server, you're defenceless."

Stallman also suggested that cloud computing is not going to be a cheap option. Users will end up paying more for their computing time than if they managed their systems themselves, he said.