back door
后门

back door: an undocumented way to get access to a computer system or the data it contains
back door: an entrance at the rear of a building
back door: a secret or underhand means of access (to a place or a position); "he got his job through the back door"

【e.g.】
He is not intelligent, so he entered Harvard through the back door.
他并不聪明,因此他是以走后门的方式进入哈佛大学。

后门（漏洞）-计算机常用词汇

A backdoor in a computer system is a method of bypassing normal authentication or obtaining remote access to a computer, while intended to remain hidden to casual inspection. The backdoor may take the form of an installed program (e.g., Back Orifice) or could be a modification to a legitimate program.