The Rise of Proprietary Software

Through the 1970s, users of "mainframes" (such as IBM's System/360 and System/370) continued to employ programmers and system engineers, and "mission critical" software and technology that generated competitive advantage were protected by keeping them secret. (Computers were operated by corporate employees, so even the capabilities were hard for outsiders to observe.)
The Apple II personal computer in 1974, the invention of the spreadsheet (sold as Visicalc) in 1976, and then the introduction of the IBM PC in 1981, created a huge market for software that was delivered to users who could study its external operation ("user interface") and "reverse engineer" internal data structures and algorithms.
This resulted in companies looking for legal methods to prevent rivals from copying the software (as "bits") and the implementation techniques (interfaces, data structures, and algorithms). Trademark and copyright claims were common starting in the mid-1970s, and in the early 1980s the U.S. decided that patents could be issued on software and "business methods".
Programmers pushed back, and created the "free software" and "open source" movements.