Johansen, 19, was 15 when he allegedly co-authored and distributed free of charge a program called DeCSS, which is used to compromise the Content Scramble System (CSS), a copy-protection system found on DVDs, designed to prevent unauthorised duplication of their content.
The teenager was accused of violating a Norwegian data security law prohibiting the unauthorised compromising of computer security systems. The maximum penalty for the offence is two years' imprisonment and fines, although prosecutors had asked for a 90-day suspended sentence.
Johansen claimed he was sent DVD security codes from abroad by other hackers and that he only combined them to create a program enabling him to watch DVDs on his Linux-based computer which, unlike computers running Windows, lacked DVD-viewing software. The teenager also said that he only used the program once, to view two DVDs he bought legally.
The movie studios argued that that the DeCSS program can also be used to copy DVDs and share the movie files on the internet, and therefore violated copyright laws.
The three-member Oslo court, however, found no evidence that Johansen used the decryption code with the intention to contribute to illegal DVD-copying or to help other individuals break the law.
The judges pointed out that Johansen used the code on DVDs he bought legally. They rejected the prosecutors' claims, reasoning that consumers cannot be convicted for "breaking into their own property."
The court also ruled that consumers have the right to access and view legally-bought DVDs however they want, even in ways different than the makers had foreseen.
The prosecutors are currently considering whether they will appeal the ruling, according to media reports.