Internet censorship

Internet censorship is control or suppression of the publishing or accessing of information on the Internet. The legal issues are similar to offline censorship.
One difference is that national borders are more permeable online: residents of a country that bans certain information can find it on websites hosted outside the country. A government can try to prevent its citizens from viewing these even if it has no control over the websites themselves.
Filtering can be based on a blacklist or be dynamic. In the case of a blacklist, that list is usually not published. The list may be produced manually or automatically.
Barring total control on Internet-connected computers, such as in North Korea, total censorship of information on the Internet is very difficult (or impossible) to achieve due to the underlying distributed technology of the Internet. Pseudonymity and data havens (such as Freenet) allow unconditional free speech, as the technology guarantees that material cannot be removed and the author of any information is impossible to link to a physical identity or organization.
In November 2007, "Father of the Internet" Vint Cerf stated that he sees Government-led control of the Internet failing due to private ownership.

Source : www.wikipedia.com