"I am continually shocked and appalled at the details people voluntarily post online about themselves." So says Jon Callas, chief security officer at PGP, a Silicon Valley-based maker of encryption software. He is far from alone in noticing that fast-growing social networking websites such as MySpace and Friendster are a snoop's dream.

New Scientist has discovered that Pentagon's National Security Agency, which specialises in eavesdropping and code-breaking, is funding research into the mass harvesting of the information that people post about themselves on social networks. And it could harness advances in internet technology - specifically the forthcoming "semantic web" championed by the web standards organisation W3C - to combine data from social networking websites with details such as banking, retail and property records, allowing the NSA to build extensive, all-embracing personal profiles of individuals...

By adding online social networking data to its phone analyses, the NSA could connect people at deeper levels, through shared activities, such as taking flying lessons. Typically, online social networking sites ask members to enter details of their immediate and extended circles of friends, whose blogs they might follow. People often list other facets of their personality including political, sexual, entertainment, media and sporting preferences too. Some go much further, and a few have lost their jobs by publicly describing drinking and drug-taking exploits. Young people have even been barred from the orthodox religious colleges that they are enrolled in for revealing online that they are gay.

"You should always assume anything you write online is stapled to your resumé. People don't realise you get Googled just to get a job interview these days," says Callas.