Police entering a home with a search warrant have no right to examine any computers they find unless a judge has given them specific permission, the Supreme Court of Canada has ruled unanimously.

In a British Columbia case involving a man police suspected of diverting electricity from B.C. Hydro for a marijuana-growing operation, a judge had granted a search warrant that made no mention of access to computers. The police seized two computers anyway in an attempt to prove that the man, Vu Thanh Long, lived in the house. The trial judge threw out that evidence, saying that in the digital age, it was inconceivable a warrant could implicitly authorize a computer search.

The Supreme Court agreed, saying on Thursday the traditional rule of authorized searches – that it is fair game to look inside cupboards and filing cabinets – needs updating for the Internet age. The computer, in effect, needs to be treated as a separate place from a home.

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"It is difficult to imagine a more intrusive invasion of privacy than the search of a personal or home computer," Justice Thomas Cromwell wrote for the court. "Computers potentially give police access to an almost unlimited universe of information that users cannot control, that they may not even be aware of, may have tried to erase and which may not be, in any meaningful sense, located in the place of search."

If they do not have a warrant specifying a computer search, police are entitled to seize and hold computers while they seek a judge's authorization to look at their contents, the court said.

However, the court said the evidence from the computers in Mr. Long's case, although illegally obtained, can be used in his trial because police acted reasonably in an area of law that was changing.

Under Canadian law, evidence that has been gathered illegally may be allowed if a judge rules that it would hurt the justice system's reputation more to leave it out.

Benjamin Berger, a law professor at York University's Osgoode Hall Law School, called the ruling a "strong and appropriate protection of privacy rights in light of the reality of the way we communicate and store information." Even highly intrusive searches of a home may not reveal as much personal information as a search of a computer, he said.