A Norwegian man cleared earlier this year of making a DVD pirating program when he was 15, has pleaded not guilty in a landmark appeal of the case.
Mr Johansen claimed he was expressing intellectual freedom
Jon Johansen, 20, is accused of breaking Norwegian law by cracking DVD codes and helping others copy films.
In January this year, he was acquitted after courts said he did not break the law when he created his DeCSS system.
The case is seen as a major test of Norway's computer protection laws, and a verdict is expected early 2004.
Mr Johansen, nicknamed "DVD Jon" by the net community, created his program to watch films on a Linux-based computer, without the need for DVD-viewing software.
He then posted the program onto the net in 1999.
It worked by getting around what is known as the Content Scrambling System (CSS) which the film industry uses to stop illegal copying.
The Motion Picture Association of America and the DVD Copy Control Association that licenses CSS complained that Mr Johansen had violated the law by doing so.
Prosecutors for the US movie industry will now try to argue that the court's interpretation of the law was not accurate in the original case, when it claimed neither Mr Johansen nor others had made use of the program to watch illegally-copied films.
Mr Johansen claims he did nothing illegal and that what he created was an expression of intellectual freedom.
The case sparked fierce debate between consumer rights campaigners and the copyright industry.
Media and film industry representatives want tighter restrictions on copying, including more digital rights management software to prevent unauthorised copying of CDs and DVDs.
This has angered campaigners because they say it prevents people from making legitimate back-ups of data.
It is claimed that piracy costs the US film industry about $3 billion (£1.7 billion) every year in lost sales.