Sweden has outlawed the downloading of copyrighted movies, games and music in an attempt to curb rampant piracy.
About 10% of Swedes freely swap music, games and films on their computers, one of the highest rates in the world.
With no law banning file-sharing, Sweden had become a hotbed of piracy where films, music and software were readily swapped.
But experts believe the law will change little and that Swedes will remain rampant downloaders.
Prior to the law coming into force, Sweden was the only European nation that let people download copyrighted material for personal use.
As a result many Swedes, thanks also to the available of cheap high-speed net access, were committed downloaders. It is estimated that about 900,000 Swedes regularly downloaded movies, games and music.
It comes a day after the US Attorney General's office announced an 11-nation operation to catch and shut down net piracy groups.
But, say experts, the habit of downloading is likely to be hard to break.
"There is nothing that indicates that (the pirates) would change their behaviour," said Henrik Ponten, a spokesman for Antipiratbyran, a Swedish anti-piracy agency funded by film studios and game makers.
"A law in itself changes nothing," he said.
Antipiratbyran estimates that one in every 2,000 Swedes has received a letter telling them that they are making pirated material available from their computer. In other nations the ratio is one in every 7,000.
The change in the law was popular with most Swedish politicians. But the nation's Justice Minister said that chasing pirates would only be a priority for the police if files were being downloaded in massive quantities.
Before the new law was passed, it was only illegal to make copyrighted material available to others via the net, whereas downloading the content was allowed.
The older law is set to be tested later this year during the trial of a 27-year-old Swede, charged with illegally making a Swedish movie available from his home computer.
Mr Ponten said if the man were fined it would send a signal to many that they could continue downloading with little fear of the consequences.
Antipiratbyran's letter writing campaign has led it to being reported to Sweden's data protection agency for flouting privacy laws by tracking people down via their net address.
As a result the data protection agency has said Antipiratbyran must stop sending out letters.
"The situation in Sweden is completely unique, with this kind of counter-reaction," said Mr Ponten.
"The forces that are fighting to keep this illegal behaviour are incredibly strong."
From BBC News