Sophie Dawson, partner in communication law and IT disputes at Blake Dawson, told Lawyers Weekly that courts will have to grapple with privacy and defamation claims in the future as current generations publish more about themselves online.

"There are going to be questions when teenagers grow up about whether if, for example, they take down all their copies of material, they can reasonably expect others to keep it private," she said.

"So if one of them becomes Prime Minister, for example, [it's questionable] whether or not that person would be able to use a cause of action to say 'Well it's highly offensive to publish now messages that I posted up myself when I was a teenager'."

For criminal proceedings, checking information online in relation to witnesses is one of the first things lawyers do, said Dawson.

"I know this only anecdotally, because it's not my area of practice, but I know there are cases where people have actually given evidence in court proceedings which is incorrect and have written the truth on their Facebook sites," she said.

"So they have been caught out lying in court - they're telling the truth to their friends online and saying something different in court and so it all unravels. I think, particularly amongst young people, they don't always realise how public internet publications can be."

Criminal barrister Matt Johnston said he had used social networking sites and chatrooms to conduct background research on cases and witnesses and that a whole industry exists in the US to issue subpoenas to Facebook.

"The case which was a classic in the US was [the accused] alleged that the copper set him up and loaded him up with drugs. The defence team subpoenaed the police officer's Facebook pages and got his entire history," he said.

"When they went through the history - immediately before and after this offence - the copper was basically saying something along the lines of 'Feeling very sneaky today' and other comments. The copper was cross-examined on that material and it was ultimately put to him that he had set this bloke up and the guy was acquitted. It shows how powerful this information can be."

There have been recent cases in Australia as well. These include an anti-Semitic video posted by a man on YouTube which will be used to test West Australia's new anti-vilification laws and Facebook photos with captions such as "getting drunk" and membership of the group "I secretly want to punch slow-walking people in the back of the head" used as character evidence in New South Wales.

John Fairburn, partner in commercial litigation at Clayton Utz, said the proliferation of material online, which makes everyone a potential film-maker or publisher, also means the proliferation of evidence available.

"There are different ways that it's being used. In some cases it's evidence of a criminal act ... for example, someone films themselves speeding or a recent one where some guy filmed himself on the back of a train, hitching a ride," he said.

"It can also often be used in going to credit or character and there was also a recent example of it being used to assist in identifying persons who might have been involved in a crime - particularly gang-related crimes."

Fairburn warned that these cases demonstrated the dangers of leaving a footprint online.

"When people are posting this material thinking that it is just remaining between their friends or within a particular group, it is, in fact, available to anyone - including prosecutors and including persons who want to take steps to prevent them from doing unlawful acts," he said.

- Sarah Sharples

Check out this week's issue 438 of Lawyers Weekly to see an in-depth look at the increasing use of social networking footprints in the courtroom.