FileZilla had 600K downloads in the past week alone, 260 million total give or take. Kudos to Avast for digging this up. Hopefully between this and Chrome Web Store shenanigans there will be an elevated interest in hunting down and exposing such things and pressuring devs to be more careful (if this were an accident) and coming up with ways to root out the problem.
Or we may all be forced to turn to userscripts.org where somehow none of these problems exist...