Computer experts have warned that millions of Facebook users could inadvertently be sharing personal information online because of the way the site's privacy settings work.

A team at the University of Cambridge’s computer department has released a study that shows how public profiles on Facebook can be used to build a more complete picture of a person.

The paper, entitled Eight Friends Are Enough, shows how a computer programme can be used to piece together limited information gleaned from public profiles to build a picture of the relationships between people.

The researchers warn that this information could be used by advertisers, the government and even cyber criminals to exploit people’s personal data.

The Home Office recently confirmed that is was considering plans to “eavesdrop” on people’s internet use, monitoring conversations on social-networking sites in an effort to prevent terrorism.