(i) address space layout randomization: this is by no means impervious but it is worth doing (ii) there being several "official" Etherium clients such that if somebody hacked just one client they could not take over the whole network.
(i) address space layout randomization: this is by no means impervious but it is worth doing (ii) there being several "official" Etherium clients such that if somebody hacked just one client they could not take over the whole network.