All property is protected by law. Essentially, when you purchase any piece of property, whether it is physical goods or software, the original design is protected by law.

Intellectual property is property resulting from the fruits of mental labour.

Intellectual property laws cover the design of most products. Copies of software (and also books, music and film) are relatively simple and inexpensive to make. The copy is usually exactly the same as the original.

Furthermore, copies can readily be made by almost anyone with computing knowledge. Laws have now been passed in most countries to protect the intellectual property rights of software developers. These laws aim to encourage the development of software by ensuring software developers are financially rewarded for their intellectual efforts.

https://en.wikipedia.org/wiki/Software_license

http://study.com/academy/lesson/software-licensing-proprietary-and-free-and-open-source-licenses.html