Tom Cross[0] in this tweet[1] was the first person I saw with the distinction in calling the FBI request an exploit rather than backdoor. This Vectra Networks blog post[2] explains this distinction in better technical detail.

[0] https://en.wikipedia.org/wiki/Tom_Cross_%28computer_security... [1] https://twitter.com/_decius_/status/699932604737417216 [2] http://blog.vectranetworks.com/blog/apple-vs-the-fbi-some-po...