Infectors are rather fast, ground artillery Manti units. They're often carried by Manti Alpha or Beta Landers.
Once dropped, they run for the first GSA building they can find and shoot at it until destruction.
They're quite resistant but can be taken by GSA starfighters and dropped in the air, resulting in their instant death. Their power is not really a threat for GSA starfighters and building, but their number can change this value.
The infector attacks through a artillery style projectile and are normally used at range. Landers will often drop them off at locations where the player might not notice immediately but due to the projectile they launch the infector is easily discovered.
Infectors will not attack the player if they are flying nearby. However if the player gets close enough they will begin to be towed the infector like a allied ground unit. If the infector is picked up it will attempt to kill the player by launching its projectile to damage the player. Dropping it out of bounds or killing it when it is firing is a easy solution. You can kill it before it is deployed by simply killing the lander holding it, if at a large enough height it will become immediately destroyed.