Chatting with "friends" on social networking sites could have legal implications and turn Facebook users into their own worst enemies.

In a precedent-setting decision, a Toronto judge has ordered a man suing over injuries from a car accident to answer questions about content on his Facebook page that is off limits to the public.

Lawyers for Janice Roman, the defendant in the lawsuit, believe information posted on John Leduc's private Facebook site – normally accessible only to his approved "friends" – may be relevant to his claim an accident in Lindsay in 2004 lessened his enjoyment of life.

As a result of the ruling by Justice David Brown of Ontario's Superior Court of Justice, Leduc must now submit to cross-examination by Roman's lawyers about what his Facebook page contains.

Brown's Feb. 20 ruling also makes clear that lawyers must now explain to their clients "in appropriate cases" that postings on Facebook or other networking sites – such as MySpace, LinkedIn and even blogs – may be relevant to allegations in a lawsuit, said Tariq Remtulla, a Toronto lawyer who has been following the issue.

This could easily apply in a personal injury case in which a litigant claims his or her quality of life has been affected, Remtulla said.

"If you are alleging that, as a result of an accident, you have not been able to enjoy life the same way and there is a photo taken after the accident showing you skiing or exercising ... that could be relevant," the civil litigation and intellectual property lawyer said in an interview yesterday.

What's on Facebook might also matter in insurance cases or family law cases where there's a dispute over custody, Remtulla suggested. Photos, for example, could reveal something about a parent's living conditions.

Facebook is a free social networking website where users can set up a "personal profile" and post photos, messages, notes, music, videos and information about their interests and activities.

Users can also exercise privacy options that restrict access to authorized "friends."

Leduc chose to limit access to his site, posting only his name and picture on his public profile.

Roman's lawyers found out about his Facebook page in 2007. When they could not get access to it, they went to court, asking that he be ordered to produce its content.

Both sides in a civil lawsuit must produce any documents that could be relevant to the litigation, whether in hard copy or electronic form.

Last year, however, a Superior Court case management master dismissed the request, accusing Roman's lawyers of going on a "fishing expedition."

The master, Ronald Dash, was not prepared to conclude, on the basis of what little information existed on Leduc's public Facebook profile, that what remained hidden from view was relevant.

Dash likened it to a diary or photo album. Just because they exist doesn't mean they contain relevant information, he said.

But Brown took a different view.

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"Facebook profiles are not designed to function as diaries; they enable users to construct personal networks or communities of `friends' with whom they can share information about themselves, and on which `friends' can post information about the user," he said.

A court can infer that Leduc's Facebook site "likely contains some content relevant to the issue of how Mr. Leduc has been able to lead his life since the accident," Brown said.

Brown said Leduc can't "hide behind self-set privacy controls" on a website that's all about telling others about one's life.