In the film industry, unsimulated sex is the presentation of sex scenes in which actors genuinely perform the depicted sex acts, rather than simulating them. Although it is ubiquitous in films intended as pornographic, it is very uncommon in other films. At one time in the United States, such scenes were restricted by law and self-imposed industry standards such as the Motion Picture Production Code. Films showing explicit sexual activity were confined to privately distributed underground films, such as stag films or "porn loops". In the 1960s, social attitudes about sex began to shift, and sexually explicit films were decriminalized in many countries.