At the time it was released, the ratings system was quite different than it is in 2012. The only ratings were "G (General)," "M (Mature)," "R (Restricted)," and "X." "M" and "R" were roughly synonymous-- both denoted "adult" content, with anyone being admitted to M rated films and R rated films requiring an adult to accompany anyone under 16. "X" rated films were those considered "too extreme" for anyone under 16, and denoted that theaters were not to permit anyone under the age of 16 even with a guardian. To this end, the sexual violence featured in the first thirty minutes of the film, and the "Ludovico Treatment" rape footage, were considered too graphic for anyone under 16 to see, hence the "X" rating. Because the X rating was not copyrighted by the MPAA, it could be used by any film distributor, and the adult film industry began to self-rate its own films "X" in order to avoid having to submit them to the MPAA for rating and face the films being banned outright due to anti-pornography laws in the early 1970s. Soon, the "X" became a marketing tool for the pornography industry, with (imaginary) ratings of XX and XXX being given to adult films by their producers to denote levels of sexual "extremity." In response, the MPAA, for all intents and purposes, ceased using the X rating for non-pornographic films; "A Clockwork Orange" and "Midnight Cowboy," two mainstream films which had been given the X rating for sexually explicit content (only to win rave critical reviews) were summarily re-rated R without any changes made to their content. In 1972, the "M" rating was replaced by "PG," marking a clearer middle-ground between "G" and "R" than the "M" rating had indicated.