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Demonstrators took to the streets of Warsaw to protest against the anti-internet piracy Acta law, which will be signed by Poland's government.

More than 1,000 people gathered in central Warsaw, some wearing Guy Fawkes masks and chanting "down with censorship". Poland's support for the Anti-Counterfeiting Trade Agreement (Acta) has sparked fury on social media.

Protesters fear that Acta, which is to be ratified by the European Union, will be as pernicious as Sopa, the Stop Online Privacy Act which was withdrawn by the White House and the US Senate after a mass protest by hundreds of major user-generated content websites.

According to the Electronic Frontier Foundation (EFF), the bill will deal primarily with counterfeit physical goods such as medicine. But experts claim it will have broader scope and will deal with new tools targeting "internet distribution and information technology". It spans all the countries in the developed world, including the EU, US, Switzerland and Japan.

The Polish branch of hacker collective Anonymous has attacked Polish government websites, including the prime minister's office, leaving several paralysed.

Anonymous released a statement on Pastebin warning: "Polish government - we are more powerful than you. We have a lot of your files and personal information. We warn you to exercise caution."

But Prime Minister Donald Tusk confirmed that Acta would be signed by Poland's ambassador to Japan in Tokyo. Government spokesperson, Pawel Gras, said Poland would sign up but it was up to national parliaments to ratify it.

Anonymous pleged to continue attacking Polish governement websites. "Dear Polish government, we will continue to disrupt and interfere with your government official websites until the 26th. Do not pass," tweeted Acta SGT Secondary.

Musician Pawel Kukiz, lead singer of the band Piersi, accused the Polish government of acting like a communist regime because it had not consulted representatives of the creative industries before agreeing to sign.

"The communists always knew what was best for people," he told the Dziennik Polska newspaper as reported by TheNews.pl website