The latest update on the official website was targeted towards cheaters who use Bots, and other means of thirds party software, to play at an unfair advantage.
Niantic has started to take action against players who abuse the system by terminating accounts completely. Whenever the system founds out that a person is cheating, Niantic will send the user stating the termination of the account.
There are several reports made regarding cheaters with GPS location spoofing (with the help of FakeGPS app) to conquer PokeGyms around the globe, and some users were reported using a mobile emulator called BlueStacks which allow users to play Pokemon Go on computers.
Prior to this update Niantic developers only apply "soft bans" towards cheaters. "Soft Bans" typically restrict users from catching Pokemon or collecting items from the PokeStops for a period of time. However, this soft ban can be removed by continuously going into a particular PokeStop, swipe, and exit until you get items from the PokeStop. The following video will demonstrate the process of bypassing the "soft ban".
However, if a users' account has been terminated incorrectly, a report should be filed on the Pokemon Go Help Center.