His next movie was one of his most famous and also his most controversial. The movie was titled "A Clockwork Orange" and was released in 1971. The movie was darker than "2001" and was originally released with an "X" motion picture rating in the US. The movie was based on a novel of the same title by the author Anthony Burgess. The novel and movie are about a criminal who is given a new and experimental 'cure' for his violent nature. The story asks questions about how society defines morality. The movie had an amount of sex and violence that was not often seen in big Hollywood movies at the time. The controversy of the movie increased when other people copied some of the acts that were committed by the characters in the movie. Kubrick and his family received violent threats from people, called death threats. These threats were serious enough that Kubrick took the movie out of theaters in Britain. The movie was not shown again in Britain until the year 2000, after Kubrick's death.