AFP said that cyber-activists attacked the websites of Finnish anti-piracy groups after a local Internet service provider was forced to block access to a popular file-sharing website.

A group of hacker activists, or "hacktivists," known as Anonymous Finland claimed responsibility on the microblogging site Twitter for the attacks, insisting about the CIAPC site: "We'll keep it down as long as we want".

"We know about it ... We are following what's happening," police investigator Timo Piiroinen told AFP, adding that such cases are "extremely challenging."