Is a sophisticated, possibly long-running computer hack that is perpetrated by large, well-funded organizations such as governments.

An advanced persistent threat (APT)

Explanation:

An advanced persistent threat (APT) is a long term and targeted cyber attack which is used to have access on a private network secretly for a period of time .The purpose of ATP is to monitor what ever activity that happen in that network without causing any harm in that network.

ATP usually attacks organization in national defence,manufacturing and financial industry because these are companies with very sensitive information which is highly valued by the state such as military plans and other values government information and enterprise organization.