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The main, and some would say the only proper, use of the word dongle is to refer to a variety of hardware device that is used as security to safeguard proprietary software. Some use dongle, by extension, to refer to any key required for a program to operate. Some extend it in a different direction to refer to any small hardware device similar in size and shape to a dongle in the first sense and that connects to a computer port. A fourth meaning is a special adaptor cable for connecting wireless cards to an Ethernet jack. In any case, the name is said to have arisen from a variation on the word dangle, which describes how the devices hang from the computer port they are attached to.
The first kind of dongle is also known as a hardware key. Without the dongle, the software cannot be run. For many dongles, this is because the software application, upon opening, sends a code to the dongle, which is meant to respond with the serial number that unlocks the product. If this transaction is not completed, the software program is not available for use, so only an authorized user can access the program, unless the device is lost or stolen. On other dongles, like the KEYLOK®, a portion of the executable code of the program may actually be stored on the dongle as another approach. In either case, for a user who has many licenses, the cost in lost time of a dongle being lost or stolen can be extremely high.
Early hardware keys were made for parallel ports. There are now various different types of dongles that take advantage of different technologies. Examples include dongles for USB and serial ports. There are also dongles that combine hardware key function with other functions, such as flash memory. In addition KEYLOCK® has a hardware key that has networking capability and can control how many concurrent users are allowed.
Dongles holding various licenses that are needed simultaneously can be daisy-chained using one port. An iLok® is one example of a dongle that can handle multiple licenses. It is a USB device that can hold up to 100 licenses for iLok®-protected software. iLok® copy protection is widely used by makers of digital audio and video software, including Mark of the Unicorn®, M-Audio®, Digidesign®, and Synthogy®. A Dongle Buddy® extends the reach of the dongle. iLok® offers Zero DownTime® protection — which, however, may not cover all the software licenses a user owns — and a loop for attaching an anti-theft cable.