Corrupted zones = ruined terrain on the map where runes are/were

No, just the area where the shadow stone date (the initial corrupted zone) and you actually need to be on the zone when you get the kill

I found that loot lake island is the best place to get the challenge done. As long as it is over a corruption zone it should count.

I'm a bit unsure of what the corrupted zones actually are. Earlier I got a kill in the area between shifty and greasy, but it didn't count. Do I have to actually kill people by the floating islands?

Eliminate Opponents by Corrupted Zones Challenge Question