| refimprove=March 2008
| cleanup=July 2009
A software protection dongle is a small piece of hardware that plugs into an electrical connector on a computer and serves as an electronic "key" for a piece of software; the program will only run when the dongle is plugged in. The term "dongle" was originally used to refer only to software-protection dongles; however, currently "dongle" is often used to refer to any small piece of hardware that plugs into a computer. This article is limited in scope to dongles used for the purpose of copy protection or authentication of software to be used on that system.
Electrically, dongles mostly appear as two-interface security tokens with transient data flow that does not interfere with other dongle functions and a pull communication that reads security data from the dongle. These are used by some proprietary vendors as a form of copy protection or digital rights management, because it is generally harder to replicate a dongle than to copy the software it authenticates. Without the dongle, the software may run only in a restricted mode, or not at all. As of July 26, 2010 it is legal in the United States to use programs protected by this method without a dongle, if the dongle is no longer working and a replacement not available.