The owner of proprietary software exercises certain
exclusive rights over the software. The owner can restrict the use, inspection of source code, modification of source code, and redistribution.
Use of the software Vendors typically limit the number of computers on which software can be used, and prohibit the user from installing the software on extra computers. Restricted use is sometimes enforced through a technical measure, such as
product activation, a
product key or serial number, a
hardware key, or
copy protection. Vendors may also distribute versions that remove particular features, or versions which allow only certain fields of endeavor, such as non-commercial, educational, or non-profit use. Use restrictions vary by license: •
Windows Vista Starter is restricted to running a maximum of three concurrent applications. • The retail edition of
Microsoft Office Home and Student 2007 is limited to non-commercial use on up to three devices in one household. •
Windows XP can be installed on one computer, and limits the number of network file sharing connections to 10. The
Home Edition disables features present in Windows XP Professional. • Traditionally,
Adobe licenses are limited to one user, but allow the user to install a second copy on a home computer or laptop. This is no longer true with the switching to Creative Cloud. •
iWork '09, Apple's productivity suite, is available in a five-user family pack, for use on up to five computers in a household.
Inspection and modification of source code Vendors typically distribute proprietary software in
compiled form, usually the
machine language understood by the computer's
central processing unit. They typically retain the
source code, or human-readable version of the software, often written in a
higher level programming language. This scheme is often referred to as closed source. While most proprietary software is distributed without the source code, some vendors distribute the source code or otherwise make it available to customers. For example, users who have purchased a license for the Internet forum software
vBulletin can modify the source for their own site but cannot redistribute it. This is true for many web applications, which must be in source code form when being run by a web server. The source code is covered by a
non-disclosure agreement or a license that allows, for example, study and modification, but not redistribution. The text-based email client
Pine and certain implementations of
Secure Shell are distributed with proprietary licenses that make the source code available.Some licenses for proprietary software allow distributing changes to the source code, but only to others licensed for the product, and some of those modifications are eventually picked up by the vendor. Some governments fear that proprietary software may include
defects or
malicious features which would compromise sensitive information. In 2003 Microsoft established a Government Security Program (GSP) to allow governments to view source code and Microsoft security documentation, of which the
Chinese government was an early participant. The program is part of Microsoft's broader
Shared Source Initiative which provides source code access for some products. The Reference Source License (Ms-RSL) and Limited Public License (Ms-LPL) are proprietary software licenses where the source code is
made available. Governments have also been accused of adding such malware to software themselves. According to documents released by
Edward Snowden, the
NSA has used covert partnerships with software companies to make commercial encryption software exploitable to eavesdropping, or to insert
backdoors. Software vendors sometimes use
obfuscated code to impede users who would
reverse engineer the software. This is particularly common with certain
programming languages. For example, the
bytecode for programs written in
Java can be easily
decompiled to somewhat usable code, and the source code for programs written in
scripting languages such as
PHP or
JavaScript is available at
run time.
Redistribution Proprietary software vendors can prohibit the users from sharing the software with others. Another unique license is required for another party to use the software. In the case of proprietary software with source code available, the vendor may also prohibit customers from distributing their modifications to the source code.
Shareware is closed-source software whose owner encourages redistribution at no cost, but which the user sometimes must pay to use after a trial period. The fee usually allows use by a single user or computer. In some cases, software features are restricted during or after the trial period, a practice sometimes called
crippleware. == Interoperability with software and hardware ==