If you do something naughty, all squads deployed gain corruption. (Araghast basically does everything but show his arse to you in the briefing, which upsets Avitus slightly) So if you don't take Avitus along to fight Araghast, he gains corruption. If you don't take a certain squad on a specific mission, they gain corruption. If the commander is corrupt, squads that deploy with less corruption gain points Your squads gain corruption in a few ways.
