Backdoor
WordNet
noun
(1) A secret or underhand means of access (to a place or a position)
"He got his job through the back door"
(2) An entrance at the rear of a building
(3) An undocumented way to get access to a computer system or the data it contains
WiktionaryText
Noun
- An unprotected passageway by which a criminal can gain access to (an assumed to be) secure area.
- Anal sex.