Updated

Poland's government went into defense mode on Monday after a network of online activists paralyzed government websites in opposition to Warsaw's plans to sign an international copyright treaty.

Poland had originally planned to sign the Anti-Counterfeiting Trade Agreement, or ACTA, in Tokyo on Thursday. ACTA is a far-reaching international agreement that would fight copyright infringement and online piracy. Critics fear it could lead to censorship on the Internet.

A Twitter account using the name "AnonymousWiki" announced plans to attack government websites to protest the government's support for ACTA.

Within hours on Sunday, the websites of the prime minister, parliament and other government offices were unreachable or sluggish, the hallmarks of a denial of service attack. The technique works by directing streams of bogus traffic at a website, jamming it in the same way that a telephone line can be overwhelmed by hundreds of prank calls.

In an initial response, government spokesman Pawel Gras on Sunday suggested there hadn't been an attack at all on the sites. "This isn't an attack by hackers, but just the result of huge interest in the sites of the prime minister and parliament," he said, a comment that quickly became a source of ridicule on Facebook and other Internet sites.

By Monday, with the sites still paralyzed, the prime minister and other leaders were holding a meeting to reconsider their stance on the treaty.

"It was a velvet attack by hackers, but still it was an attack. Pawel Gras was wrong," said Slawomir Neumann, a lawmaker with the government Civic Platform party. Neumann said the situation showed that the Polish government is poorly prepared to handle such attacks.

And Michal Boni, the minister for administration and digitization, acknowledged in a radio interview Monday that the government had failed to hold enough consultations with the public on the matter.

An opposition party, the Democratic Left Alliance, also called on the government to not sign in it in a gesture of solidarity with those who warn it could hurt Internet freedom.

Anonymous, the group suspected of involvement in the attacks, made a number of threats before and during the Internet disruptions.

"Dear Polish government, we will continue to disrupt and interfere with your government official websites until the 26th. Do not pass ACTA," one tweet by AnonymousWiki said.

It also threatened more trouble should Poland sign ACTA.

"We have dox files and leaked documentations on many Poland officials, if ACTA is passed, we will release these documents," AnonymousWiki said in a separate tweet.