WARSAW, Poland — Protesters took to the freezing cold streets of Berlin, Helsinki and many other European cities Saturday to voice anger at an international copyright treaty they fear will lead to censorship and a loss of privacy on the Internet.

The rallies across the continent underline how opposition to the Anti-Counterfeiting Trade Agreement, or ACTA, has spread quickly since a first groundswell of opposition emerged last month in Poland.

"We have the protests in Poland to thank above all for what is happening in Europe and worldwide at the moment," said Tillmann Mueller-Kuckelberg, an organizer at a protest in Berlin.

"A lot of people in other European countries woke up then, and we hope worldwide that the protests will lead to the ACTA agreement being stopped."

ACTA has been under negotiation for years and has already been signed by a number of industrialized countries, including the United States, South Korea and Japan. Its drafters say it is needed to harmonize international standards to protect the rights of those who produce music, movies, pharmaceuticals, fashion, and a range of other products that often fall victim to piracy and intellectual property theft.

Several European countries recently signed ACTA but ratification remains in question in some countries as contempt builds toward it, mostly from young people who fear it will lead to censorship online and block their access to information.

The Polish and Czech governments have signed, but put ratification plans on hold, while Germany said Friday that it would delay signing to give time for discussions.

ACTA shares some similarities with the hotly debated Stop Online Piracy Act in the U.S., which was shelved weeks ago by lawmakers after a swell of opposition that included Wikipedia and Google blacking out or partially obscuring their websites for a day in protest.

In Germany, a few thousand people protested in downtown Berlin Saturday, some sticking tape over their mouths or wearing Guy Fawkes masks, which have become a symbol of the Internet activist group Anonymous and now the anti-ACTA movement. They carried placards such as "Stop ACTA," "Right to Remix" and "ACTA: the rule of law was yesterday."

Mueller-Kuckelberg, the Berlin organizer, said the movement against the agreement was "a broad civil rights alliance that has come together out of spontaneous outrage at this project."

Several thousand people also demonstrated in Munich, while there were also protests of 1,000 people or more in Frankfurt, Nuremberg, Hannover and Augsburg.

Germany's Foreign Ministry said Friday that the country had held off on signing ACTA after the Justice Ministry voiced concerns. An official signature is needed before the deal can go to Parliament for approval.

The European Parliament is set to debate the legislation early this summer.

Rallies also took place in Paris, Vienna and many other cities.

"The bad thing about ACTA is the totally undemocratic approach," said Thomas Lohninger, an Internet activist and moderator at the Vienna event, which drew 2,500 people. "It can't be that a law is passed in such a way, especially if it affects our Internet freedoms so significantly. It must be stopped."

In Lithuania, hundreds rallied in front of a government building in Vilnius, some carrying signs that said "Stop ACTA."

"We are deeply concerned about this controversial deal, which most of our society does not know anything about," said Mantas Kondratavicius, leader of the Vilnius Liberal Youth organization, a rights group.

"There was no public presentation or debates on the principles and possible threats of this act," Kondratavicius added.

Many critics are angry that ACTA was negotiated by politicians in secret, without involving civic society.

About 5,000 Bulgarians marched in their capital, Sofia, most of them young people and some also wearing Guy Fawkes masks, while rallies also took place in other major Bulgarian cities.

"Stop ACTA or we will stop it," read one poster in Sofia.

In the Czech capital, Prague, hundreds rallied at the medieval Old Town Square while a similar crowd gathered in the second largest city, Brno. They waved banners that read: "ACTA stinks," "ACTA harms you" and "ACTA equals cyber fascism."

The government has suspended the ratification of the treaty and the protesters welcomed the move but say it is not enough.

Marches also took place in several Polish cities, including Warsaw, Szczecin, Poznan and Gdansk.

"Down with the censorship of Big Brother," said one of the banners in Warsaw.