Queensland-based criminal defence lawyer Bill Potts said social networking sites such as Facebook and Twitter are becoming a "goldmine" for police and lawyers, as people post information about their activities online and unwittingly incriminate themselves.

Potts, a director at Potts Lawyers, used the recent example of a Queensland man who used Facebook to brag about an assault and home invasion and was subsequently jailed for six years.

"Even if social network posts are in theory hidden behind privacy settings, police can still monitor them. Prosecutors are increasingly looking at Facebook for evidence of crimes that can carry significant jail time," he said.

Two British men were jailed recently for trying to incite riots using Facebook, and Potts said he expects Australian police will begin to make more use of evidence from social networking sites.

"However private you think your posts are, they can be easily accessed by police," he said.

"It's amazing how people are unthinkingly sharing not just words but images of themselves doing potentially illegal things, blissfully ignorant that the police could later access it for evidence."

Potts said defence lawyers are also monitoring social network sites for information which might be useful in court.

However, Potts said that because phone recordings, intercepted emails and texts are able to be manipulated, he would expect that such evidence would be vigorously tested.

"Defence lawyers would want to investigate whether the posts on a social network site, or sound recordings and emails had been edited or tampered with. Evidence from phone or electronic taps is going to complicate trials and also be a fertile breeding ground for appeals," he said.