Question

If your computer has a ________, someone else can gain access to it undetected.

Answer 1

If your computer has a rootkit, someone else can gain access to it undetected.
The term rootkit denotes a set of software tools typically malicious.
 The purpose of this software is to enable access to a computer or areas of its software that is not otherwise allowed.
It is one of the most difficult types of malware to find and remove.