Calling it an attack is a bit weird. Attacks are typically meant to things like create double spends. An hard fork is the natural mechanism for a blockchain to

Calling it an attack is a bit weird. Attacks are typically meant to things like create double spends. An hard fork is the natural mechanism for a blockchain to update. The Homestead release for example was an update that was done through an HF, the next update Metropolis will also be done through a HF. For the DAO HF: The DAO contract was replaced by a withdrawal one, that was the only change, No other contract broke because of the fork.