destroying mining big farm will effectively put a serious dent on bitcoin,  and since you can not build a peta farm in few days, the network would be at 51% risk from random miners in the world

this is the only real thing that can make bitcoin unsecure for me, it's not that hard for terrorist to attack a farm for example if they want to, they just have no reason to do it currently

i don't know how much they invested in personal security but i doubt it's strong enough