Even opponents of Hadopi acknowledge that the law has resulted in a change in online behavior, though they dispute whether its effect on music industry sales has been beneficial.

Jérémie Zimmermann, co-founder of La Quadrature du Net, a group that campaigns against restrictions on the Internet, said the law had resulted in increased use of virtual private network software and other anonymity tools.

“Apparently some of its intimidation is having a psychological effect,” he said of the three-strikes law, but added: “The political costs of creating an institution like this are tremendous.”

Stories like that of Robert Thollot, a teacher who lives near Saint-Étienne, in central France, have not helped. Mr. Thollot was accused of illegally downloading songs by David Guetta and Rihanna, as well as the film “Iron Man 2.”