In what ways could "bitcoin" be hacked? Dan Kaminsky said that he spent 4 months trying to hack "bitcoin" but failed.

Besides trying to find vulnerabilities in double-spending and 51% attack, what other hacks would a hacker try to achieve?

Surely an established hacker like Dan Kaminsky wouldn't have spent 4 months just trying to prove the protocol is immune to double-spending and robust against 51% attacks. There had got to be more things that he was trying.

Exactly what kind of hacks will a hacker try to achieve against bitcoin?
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.