Websites that link to offensive material may no longer be able to hide behind the defence that they are not technically publishers, after an Australian man successfully sued Google for defamation.
Michael Trkulja won a landmark defamation case against the technology giant over search results that linked him to underworld figure Tony Mokbel.
Mr Trkulja has never been involved in criminal activity, but was shot in the back at a restaurant in Melbourne during gangland wars in 2004. This case led to the now defunct website Melbourne Crime publishing photos labelled with his name.
Mr Trkulja asked Google to remove the content in 2009, but the company failed to do so. Legal experts believe this could set a precedent for future cases.
"They have to take some responsibility for what passes through their search systems, for what they index," said Mr Trkulja's barrister Christopher Dibb.
Mr Dibb said there is no reason why the same would not apply to social networks such as Facebook and Twitter, if they were issued with a takedown notice.
Simon Rigby, a partner at Holman Webb lawyers who specialises in defamation law, agrees.
"The implication for the future is that companies can't carry material on the internet with impunity," he said.
"What this means for the likes of Google and Yahoo is that when they get a takedown notice they have to respond to it or face the consequences."
But Jim Davis, Emeritus Professor at the Australian National University's College of Law, said that Google was only liable because it failed to respond to Mr Trkulja's complaint.
The defence of innocent dissemination failed because Google was aware of the defamatory material.
But he agreed that internet companies cannot ignore takedown notices.
"This is a good lesson for Google and for any other search engine that if people complain, then the wisest course of action is to take the material down," he said.
Similar cases in the UK have ruled that search engines are purely mechanical devices and are not responsible for the material published.
However, in March Mr Trkulja won a similar case against Yahoo!, which accepted that if someone accessed material through Yahoo! then they were publishers. Mr Trkulja was awarded $225,000 in damages from that case.
The Supreme Court's Justice David Beach is expected to deliver a ruling on damages on Monday week.
Google declined to comment on the ruling.