They developed their own proof-of-work system to rate limit requests, using SHA256, implementation details here: https://archive.is/dfBVN https://archive.is/dfB

They developed their own proof-of-work system to rate limit requests, using SHA256, implementation details here: https://archive.is/dfBVN https://archive.is/dfBVN They also have servers in multiple countries. Some of these servers being blackholed by Cogent, by the way.