cialis 40mg http://currencyaffairs.org/wp-admin/includes/deprecated.php geneva; font-size: small;”>Users attempting to access the site see a black screen and a political statement: “Imagine a world without free knowledge.”
The user-generated news site Reddit and the blog Boing Boing are also taking part in the “blackout”.
However, Twitter has declined to join the shutdown.
Wikipedia, which attracts millions of hits every day, is opposed to the US Stop Online Piracy Act (Sopa) and Protect Intellectual Property Act (Pipa) being debated by Congress.
The legislation would allow the Justice Department and content owners to seek court orders requiring search engines to block results associated with piracy.
The site’s founder, Jimmy Wales, told the BBC: “Proponents of Sopa have characterised the opposition as being people who want to enable piracy or defend piracy”.
“But that’s not really the point. The point is the bill is so over broad and so badly written that it’s going to impact all kinds of things that, you know, don’t have anything to do with stopping piracy.”
The site was still available on mobile phones, however.
Google.com also joined the protest, blacking out its logo and linking to an online petition urging Congress to not censor the web.
It is an unprecedented protest, says the BBC’s Steve Kingstone in Washington.
Analysts say it is the first major test for the young and disorganised internet industry against powerful media interests with many lobbyists in Washington.
Sopa’s supporters in the House of Representatives say the legislation is designed to stop revenue flowing to “rogue websites”. A similar bill, Pipa, is making its way through the US Senate.
On Saturday the White House issued a statement that appeared to side with critics of the legislation.
It said: “While we believe that online piracy by foreign websites is a serious problem that requires a serious legislative response, we will not support legislation that reduces freedom of expression, increases cybersecurity risk, or undermines the dynamic, innovative global internet.”
Sopa and Pipa explained
The US bills are designed to block access to sites containing unauthorised copyright material.
Content owners and the US government would be given the power to request court orders to shut down sites associated with piracy.
Advertisers, payment processors and internet service providers would be forbidden from doing business with infringers based overseas.
Sopa also requires search engines to remove foreign infringing sites from their results, a provision absent in Pipa.
Full explanation on Sopa and Pipa
Despite the hint of a presidential veto, Wikipedia said that the English site’s administrators had decided to stage its first ever public protest because the bills “would be devastating to the free and open web”.
It added: “We don’t think Sopa is going away, and Pipa is still quite active. Moreover, Sopa and Pipa are just indicators of a much broader problem. All around the world, we’re seeing the development of legislation intended to fight online piracy, and regulate the internet in other ways, that hurt online freedoms.”
However, when asked whether Twitter would join the blackout, its chief executive, Dick Costolo, tweeted: “Closing a global business in reaction to single-issue national politics is foolish.”
In a Twitter conversation with Wikipedia’s founder Jimmy Wales, Mr Costolo later clarified that his comment was not meant to be read as a “value judgement” aboother organisations involvement in the action.
The anti-piracy legislation still has high-profile supporters including News Corporation’s chairman, Rupert Murdoch.