There is no exploit, they simply had enough hash power to fork it and create coins in the chain. Simply, we can remove the offending blocks that deviate from the 25B cap.
Those blocks are sold to many people. Question is who should lose money? We who bought coins or the exchange or the crackers?
Somebody deposited 23 billion coins into their account at Cryptopia. Cryptopia has to decide if those coins are legitimate.
No, somebody probably deposited almost all of the 50 billions of blockchain injected coins.
Very big part (maybe all?) of that injected coins sold at 1, 2, 3 or so litoshis before 5, 4, 3, 2, 1 months ago. Of course Cryptopia has many data too and probably they know who deposited that coins, but Cryptopia is not the court and they can't make the right decision what to do now. Few bitcoins, maybe few 10s, left the exchange, and every Cryptopia's decision would be wrong now.
Only solutions with no new injured parties is to protect the coin from the new injections, I think.