Video games are especially vulnerable to this. When the system that a game was designed for becomes obsolete the game itself is frequently forgotten entirely by its manufacturer, becoming abandonware, a kind of orphan work. Computer games have a history dating back to the 1960s, and most of the older examples of the genre are designed to be played using hardware and operating systems that are long outdated. Not only does this mean that the game becomes essentially unplayable, it can also lead to unclear or contested copyright, with ownership being claimed by or attributed to multiple individuals or entities.