Hacking collective Anonymous hacked the website of Bulgarian music industry group Prophon on February 5. Prophon collects and distributes intellectual property royalties, but also acts as lobbyist organisation.

The collective replaced the front page of Prophon's website, saying that "this domain has been seized by Anonymous under section #14 of the rules of the Internet". Other pages on the prophon.org website had been left unchanged.

"This is Anonymous. It has come to our attention that YOU and another twelve greedy organisations have signed a open letter, supporting the so-called 'Anti-Counterfeiting Trade Agreement'," the defaced front page read.

"Not only your letter is full of false statements, but you are also essentially calling people's concerns about their FREEDOM 'groundless suggestions and manipulations'. This is unacceptable, this is where you made us rage. You are the first, but not the last. This should be a lession for the other ACTA supporters."

The hacking group also posted a link to a four-minute clip from The Great Dictator, Charlie Chaplin's 1940 satire on Nazi Germany.

Bulgaria is one of 22 European Union member states to have signed ACTA, the international treaty that, online freedom groups say, opens the door to strict policing of online content. 

Following the signing ceremony on January 26, public opposition to the treaty's ratification by Bulgarian Parliament has been growing, with a protest scheduled for February 11, when similar rallies are planned in other European countries.