Logic bomb
A Logic Bomb is a piece of often-malicious code that is intentionally inserted into software. It is activated upon the host network or personal-device only when certain conditions are met, like a particular point in time, the removal of access rights of an individual (employee) or any other condition that you can think of.Many malware uses this to execute at a certain moment; adware often deploys after several system-boots and IT-personnel sometimes feel the need to "leave with a bang". The result can be anything: because the source-code only gets active when the condition is true, it might take a long time for it to be discovered.