''Imagine a world without free knowledge'' , that is the short message with which visitors to the English-language site of Wikipedia are greeted on Wednesday. The much-consulted web site has been shut down since 6am and will stay down for 24 hours. This decision is a protest move against the current discussions in US congress to pass a bill of law known as the SOPA, Stop Online Piracy Act.

The law, which is supposed to improve online protection of intellectual property, is, in fact, a way to further censor certain sites, say the people behind Wikipedia.

They see it as a fight between the old world and the new world or to use a tangible example : a fight between the entertainment industry Hollywood and Silicon Valley.

One of the main problem points Wikipedia has with the impending SOPA laws is the fact that the bill will force search engines or servers to verify that the links they lead to don't host content, which infringes on copyright. Since Wikipedia sees itself as a search engine, this would mean that the few people that run it would have to thoroughly check the 3,8m articles with links currently available on the encyclopaedia.

But Wikipedia isn't alone in seeing the dangers the SOPA-law could bring with it. A coalition of big corporations including Facebook, Google, AOL, ebay, Twitter, Kaspersky or Human Rights Watch is rejecting the controversial bill. Further protest measures are being discussed.