Computer hackers are planning to target social networking sites, such as MySpace and Facebook, in a multi-billion-pound "cyber war" next year, security experts warn.

IT professionals predict that cyber criminals will launch a campaign to gather personal information from users of the popular websites. Details including age, sex, marital status and where a person lives can be found on the sites and malicious users plan to trawl the networking websites collecting this data and picking targets for phishing scams.

According to reports hackers will also focus on people using instant messenger and telephone calls over the internet to garner sensitive information in order to steal people's identities and commit other online crime.

Graham Cluley, senior consultant at Sophos, said: "The huge popularity of sites such as MySpace means it is an increasingly attractive target for criminals, who are always looking for new ways to gather information.

"If the hackers know you have a particular interest this can be used to target you in a phishing attack. They know what you're into and can exploit this to obtain more information from you such as credit card details.

He added: "People are putting far too much information online and into the hands of identity thieves. Young people in particular, need to be very careful as it may come back to haunt them."