When the Umojan Protectorate expedition to Jarban Minor was overrun by the zerg, banshees and their pilots were infested and made to serve the Swarm. They were set up around the extraction devices, and burrowed near them to ambush would be attackers.
When Agent Nova Terra came to Jarban Minor to retrieve terrazine, she was forced to engage the infested banshees surrounding the extraction devices.
Infested banshee appear in the Nova Covert Ops mission Night Terrors. They are comparable to the normal terran banshee, but will appear from the ground once Nova's army approaches too closely. Nova's snipe, liberator anti-air, or goliaths and marines can take these out with relative ease.
When assaulting the far northwest extraction device, the zerg will send swarms of banshees at the player that focus the extraction device. However, target priority may mean anti-air liberators will focus the harder to kill corruptors first. Consider placing several missile turrets around this extractor, as they will both be a priority for the banshees and take them out with relative ease.
Infested banshees have the ability to cloak, but do not make use of it.