[a] hardware or software mechanism that (a) provides access to a system and its resources by other than the usual procedure, (b) maintainers, and (c) usually is not publicly known.[4]
[a] hole or access point left, by design, in the program by the original programmer or developer. Usually used by programmers to simplify the program-testing procedures; however, on occasion, programmers forget to close these holes or are not aware of other holes created by the original backdoor.[5]
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[a] computer system feature — which may be (a) an unintentionalflaw, (b) a mechanism deliberately installed by the system's creator, or (c) a mechanism surreptitiously installed by an intruder — that provides access to a system resource by other than the usual procedure and usually is hidden or otherwise not well-known.[6]
Another approach that gained attention in early 2016 are measures to compel companies to generate and deploysoftware updates that would defeat the encryption protections from a particular device, tool or service."[11]