YouTomb, a project of the MIT Free Culture group that studies takedown notices by the video-sharing website YouTube, has identified a mechanism used by Google to restrict video content in specific countries. This appears to be the method YouTube is using to filter videos on behalf of governments and private actors that request it.
A growing number of countries have instituted mostly short-lived blocks against YouTube for containing culturally or politically sensitive content, including Brazil, China, Morocco, Syria, Thailand and Turkey. On February 22, 2008, Pakistani ISPs were ordered to partially block YouTube reportedly in reaction to a video making fun of the Prophet Muhammad, and ended up disrupting access to the entire site for users around the world for up to a few hours. In some cases, YouTube has blocked the identified offending video(s) in that country in order to have the block lifted.