A number of high-profile web sites have taken their content offline on Wednesday to protest the controversial US Stop Online Piracy Act (SOPA), including Wikipedia, Reddit, Mozilla, WordPress and Craigslist.
Digital rights groups have also put up warning messages on their homepages.
SOPA, currently making its way through the US Congress, has received widespread opposition from the IT industry and the White House said in a statement last week that it was also against the bill.
Wikipedia took all its English speaking content offline at 5am on Wednesday morning in a protest that is planned to last 24 hours.
Readers wanting to visit the online encyclopaedia will be greeted with messages intended to raise their awareness of SOPA, which was introduced in the US House of Representatives, as well as the Protect IP Act (PIPA), introduced in the US Senate.
"Right now, the US Congress is considering legislation that could fatally damage the free and open internet," says the Wikipedia landing page.
The only articles still available in English on Wikipedia are those about SOPA and PIPA.
Mozilla will join the protest at 8am US Eastern time by blacking out its default start page in Firefox and redirecting key Mozilla web sites to a special action page.
"These bills protect content at all costs, creating the opportunity for abuse and damaging the web for all," said the firm in its company blog.
Social news site Reddit will join the protest at the same time as Mozilla and online listings site Craigslist appears to have taken its US content offline.
Meanwhile, WordPress has already blacked out all its content with censorship labels that redirect to a page giving details on why it has joined the "internet strike".
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