Until relatively recently this was a contradiction in terms. Until the late 1990s it proved very difficult to gain a patent for software in either the US or the European courts. This state of affairs has been much criticized, as a patent is easy to enforce in law since it is officially registered and no proof of copying is necessary. However, in the late 1990s, US law was liberalized and a number of landmark cases allowed the patenting of software and business processes. See also software copyright.