The Beast Infection Weapon (better known as Infection Beam) was a unique particle beam weapon that sent beast cells onto targeted ships.
Once cells reached their target they began to absorb the ship's hull and when merging with living organisms, it creates a neuron interface that allows the Beast to take control over vessels.
A charged plasma beam jumps from target to target allow the Beast to infect all nearby ships, however more massive targets degrade the jump ability of the beam. The most massive units such as destroyers or dreadnoughts are capable of stopping the beam completely after issuing the Naar Directive, which prevents the infection from spreading at the cost of some the ship's health.
The Beam could only be created on the heaviest ships, such as Heavy Cruisers, Carriers or the Beast Mothership, and would still have a very long recharge time. Despite the general rule that ships heavier than Destroyers were immune to the Beam, Qwaar-Jets were an exception and it's unknown what caused this effect. However, this could be simply be because the Models for infected destroyers and Motherships were never made. All infected ships could eventually be built by the Beast, as the technology for their construction was developed or absorbed.