Hijack

There are several folk etymologies:

That it arose from someone wanting a lift on a truck calling "Hi, Jack" (the exclamation plus the name), until this was used often as a trick by robbers.
That it comes from seamen who were robbed by prostitutes in former centuries in London. Prostitutes would call out "Hi, Jack" to passing sailors. Instead of receiving the services they expected, some sailors were instead robbed by an accomplice.
That it comes from the Old West phrase "hold 'em high, Jack"

Sourced etymologies include:

Full definition of hijack

To forcibly stop and seize control of some vehicle in order to rob it or to reach a destination (especially an airplane, truck or a boat).
To seize control of some process or resource to achieve a purpose other than its originally intended one.
(computing) To seize control of a networked computer by means of infecting it with a worm or other malware, thereby turning it into a zombie.
(computing) To change software settings without a user's knowledge so as to force that user to visit a certain web site (to hijack a browser).
(politics) To introduce an amendment deleting the contents of a bill and inserting entirely new provisions.

(plural hijacks)

An instance of hijacking; the illegal seizure of a vehicle.
An instance of a seizure and redirection of a process.
(politics) An amendment which deletes the contents of a bill and inserts entirely new provisions.
(poker slang) Preflop, the position two before the dealer.