The Intruder Missile was a special type of ordinance with a very strong ionizing effect used during the Galactic Civil War.
The Intruder Missile was originally designed by Slayn & Korpil, most commonly known for its unique vehicle designs. The initial design was distributed to Rebels during the Galactic Civil War and used aboard their B-Wing bombers as well as Z-95 Headhunters and YT-class freighters. The missile is armed with an ionizing warhead designed specifically to overload the shield generators on capital ships, causing them to explode and destroy the rest of the ship in the process. The missile was incapable of targeting anything smaller than capital ships and were much more effective if the target was being simultaneously attacked by other weapons - perhaps as a means of destabilizing the shield generators or allowing the missile to penetrate the shields and impact the hull.
In an unusual reversal of roles, ISB agents stole the design from the Rebel-sympathizing Slayn & Korpil and gave the plans to Sienar to produce the weapon for them. Perhaps as a result of this theft, Black Sun was able to acquire the missile to sell to bounty hunters and mercenaries. The Sienar-produced missile was more commonly loaded onto TIE Bombers, TIE Defenders, and freighters than other Imperial craft.