IMIPAK (occasionally referred to in apocrypha as IMIPAC) was a weapon developed by Coser. Its name stood for Induced Molecular Instability Projector And Key.
The weapon was in two parts, the projector and key. Use of the projector 'marked' an individual with an unstable molecular potential; this did not harm them and they were often unaware of it having occurred. The potential could remain indefinitely.
The key, when used, triggered the potential, killing the 'marked' individual. The key was a sophisticated unit, capable of activating the potential in specific individuals whilst leaving others alive. Its inventor claimed death was instantaneous within a range of a million miles. Blake believed the mass of a planet might block the trigger signal but this was never put to the test.
Coser praised his weapon's versatility, claiming it could be used to kill, or enslave, or as a security system - marked individuals would be forced to avoid any area where the trigger signal was continually being broadcast.
IMIPAK was single-handedly created by Coser, who killed his superiors and went into exile with it. His actions were predictable, however, and he was tricked into giving the weapon to a clone of Blake in Servalan's service. Servalan killed him with IMIPAK and used it to mark Travis, Blake, Avon and Gan.
However, before Servalan could eliminate them, she herself was marked by Rashel, who took IMIPAK and warned her to leave the planet. IMIPAK remained there, guarded by Rashel and the clone.