A man in Warsaw protesting earlier in the week against Poland's plan to sign the ACTA treaty Veronika Joy/ WBJ

Poland signed the international copyright treaty known as the Anti-Counterfeiting Trade Agreement (ACTA) on Thursday despite nationwide protests, the hacking of government websites and the threat of cyber warfare by internet users who oppose the deal.

Critics of ACTA argue that the bill, which aims to create international standards for protecting intellectual property, will stifle freedom of expression on the internet, pointing to a clause in the treaty which suggests that internet service providers (ISPs) would be obliged to give up data about users who were being accused of copyright infringement.

Earlier this week, protests against Poland's planned signing of the ACTA treaty were held in a number of cities across the country with the biggest being in Kraków. Cyber attacks were also carried out on government websites by opponents of the treaty.

But Prime Minister Donald Tusk said the government “would not submit to blackmail” and that the treaty would be signed. He added, though, that “only when the government is sure that Polish law guarantees freedom on the internet, will we send the bill for ratification to parliament.” The treaty would also need to be ratified by the Polish president before becoming law.

“ACTA was accepted by countries who, like it or not, are the backbone of freedom in the whole world, namely the EU, the US, Australia, New Zealand, Canada, South Korea and Mexico,” Poland's prime minister said.

The treaty will now have to be ratified by the European Parliament and then accepted by the European Council before it comes into law. It is expected that the European Parliament will vote on the treaty in either April or May.