While Viruses etc. are good ideas for one, and truthfully, this kind of “chain lightning” or “moon glaive” weapon would be nice indeed (or did that idea now disappear?), I cannot really say “yeah” to a “virus” which basicly “infects spaceships over the vacuum” and seems to have no natural counter even if you experience it more often; you would fail after two attempts if the ships went home and some software engineer would close the “holes” in software you misused.
Viruses just dont work this way, not today, not ever, and certainly we are over the age, where any computer related “mysticism” is easily accepted. You need a hardware vector for this, basicly something which interacts directly with the hardware and “creates the virus on the fly” inside the system.
So basicly, I would not do it as a virus, if it is about multiple infections. Instead, I would do it much like spydrones, or as additional ability for spydrones, you can activate once the target has a spydrone attached (no matter if by you or others).
I would say, you can infect a primary ship as a carrier, and “any ship which it affects / gets affected by” with aura buffs would get affected, except the carrier, resulting in the buffs simply turning off with cooldowns, much like ECM does to one target. This brings in two main things:
* first off, you need to infect an enemy and he brings havoc to his own people, by turning off all their nice buffs they try to give.
* second, your team has to let him escape back to his team.
* it deactivates any buff the carrier is exposed to. shield recharge, energy recharge, missile shields, anything turns off with cooldown. It can be instantly reactivated.
* the carrier should not be automatically notified about him being infected.
* ecm against the carrier turns off the virus too.
* directed buffs on a carrier - like shield heals - cause the virus to piggyback to the caster and is the only way to infect other ships becoming carriers themselves. This makes it ideal for captain maps.
Needlessly to say, ECM intys should have it of course - however, since I am still adamantly against a subclassing of the interceptor class so much, I would like them to be deployed on any Interceptor classed ship;
Using the same device without drones to attach them (or if they are out), gives only a chance to infect a single target and is basicly then only a half-baked ECM device. The chance is higher if the target is inside (hostile) mines, using mine control signals as carrier. An alternative would be in this case, that the mines kinda turn on their master, but well, it is complicated as it is now.
Using the device without a target lock will activate it on an active spydrone of yours.
So, for the enemy to infect others, you need spydrones to make him a carrier, and use the network bridges the buffs use to heal him to hack for you - otherwise you can use it as a general ECM, which is mainly useful against tanks in minefields. And its perfectly explainable in every detail, why it is so hard to counter it via a simple software upgrade at base. Also, since spydrones are limited on the battlefield, you cannot simply spam this, and offer it to numerous interceptor classes.