The areas where pieces of the Prometheus satellite had landed and are now quarantined by NATO. There are 116 Hot Zones world wide. Very few people are allowed in and lethal force is authorized on some Hot Zones. Not much is every heard from those stuck in. Rumors are that Section M have people in every Hot Zone.
Times Square is the largest Hot Zone.
Promethean Radiation is still present in some of them. Some theorize there's still enough to trigger a mutation.