
How the hell are people mining at 3TH/s?

O_o
That's not in the terahash realm. You're looking at a stupidly powerful system, but it's certainly not in TH/s.
Assuming a botnet with 9-11MH per physical CPU, that's a network of approximately 300,000 systems.
OR
SHA-3 ASICS!
Assuming a lame pool with exploit, they stealing other users coins.