In what ways could "bitcoin" be hacked?
There could also be hacks targeting the bitcoin software implementation. If a vulerability is applicable to software running on majority (>50% hashrate) of the nodes then it is a real threat.

For example lets say someone can craft a mal-formed transaction that somehow can trick >50% nodes to accept it (for example induce a buffer overflow and somehow allow attacker to gain remote access to the node system itself and make modifications) then bad things will happen.