A ongle is a small piece of hardware that connects to a computer. The usual function of a dongle is to authenticate a piece of software. Without the dongle, the software will run only in a restricted mode, or not at all. Dongles are used by some proprietary vendors as a form of copy prevention or digital rights management, because it is much harder to copy a dongle than to copy the software it authenticates. Despite being hardware, however, dongles are not a complete solution to the trusted client problem.