Proprietary software is software that, according to the free and open-source software community, grants its creator, publisher, or other rightsholder or rightsholder partner a legal monopoly by modern copyright and intellectual property law to exclude the recipient from freely sharing the software or modifying it, and—in some cases, as is the case with some patent-encumbered and EULA-bound software—from making use of the software on their own, thereby restricting their freedoms. Proprietary software is a subset of non-free software, a term defined in contrast to free and open-source software; non-commercial licenses such as CC BY-NC are not deemed proprietary, but are non-free. Proprietary software may either be closed-source software or source-available software. Until the late 1960s computers—large and expensive mainframe computers, machines in specially air-conditioned computer rooms—were usually leased to customers rather than sold. Service and all software available were usually supplied by manufacturers without separate charge until 1969. Computer vendors usually provided the source code for installed software to customers. Customers who developed software often made it available to the public without charge. Closed source means computer programs whose source code is not published except to licensees. It is available to be modified only by the organization that developed it and those licensed to use the software. In 1969, IBM, which had antitrust lawsuits pending against it, led an industry change by starting to charge separately for mainframe software and services, by unbundling hardware and software. Bill Gates' "Open Letter to Hobbyists" in 1976 decried computer hobbyists' rampant copyright infringement of software, particularly Microsoft's Altair BASIC interpreter, and asserted that their unauthorized use hindered his ability to produce quality software. But the legal status of software copyright, especially for object code, was not clear until the 1983 appeals court ruling in Apple Computer, Inc. v.