As stated in the AWS acceptable use policy of disallowed activities on their network:
Intentional Interference. Interfering with the proper functioning of any System, including any deliberate attempt to overload a system by mail bombing, news bombing, broadcast attacks, or flooding techniques.

Have fun tracking down one of BCX's instances. Also, this would be master debatable, clients following the longest block chain is by design, so I would argue his 51% attack would "[interfere] with the proper functioning of any System."