In the decision, believed to be the first of its kind, the court last month said those connecting a computer to the Internet must expect that outsiders will seek ways to enter their system and that it is the owners' responsibility to protect their computers.
But critics said the ruling is comparable to allowing a burglar to check all the doors and windows of a house for locks and not prosecuting them until they actually break in.
In theory, hackers in Norway can now legally search computers anywhere in the world for security holes. Such information could then be passed on to other hackers for possible illegal use.
The ruling arose from a 1995 case against a company that specializes in computer security. An Oslo-based company, Norman Data Defense Systems, sought ways to break into the University of Oslo's computers through the Internet for a news report by the Norwegian state broadcasting network NRK.
Norman attorney Kai Thoergersen said in an interview Wednesday that the company simply mapped holes in the computers' security systems, without breaking in, tampering or stealing any information.
The university sued, and a lower court ordered Norman to pay $13,500 for violating a law against hacking into computers. Norman appealed, and the case reached the Supreme Court, which dismissed the fine, partly because the company had not broken into the computer.
Norman claimed it did nothing more than what any Internet users do each time they search the global network for information.
However, Arne Laukholm, director of Information Technology for the University of Oslo, said the ruling opens the way for systematic and malicious attacks on computers. He said protecting computers hooked up to the global network against such hacking is difficult and expensive.
Dave Farber, a computer expert at the University of Pennsylvania, called it "a bad precedent" that could allow hackers to operate legally in Norway, even if their actions violated other nations' laws.
The ruling was made Dec. 15, but the court did not publish its basis for the decision until this month.
Reported By Doug Mellgren.
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