I'm not a hacker, but I guess it could have been done. if the skill that they have been very great, it's not a difficult thing. but, the thing is, if they want to take your bitcoin or not? because I think they are always eyeing bigger things, such as trading sites, or the like, which can make them a profit enormously.
I don't think that they can hack huge amount if bitcoin if they want because if it were so, bitcoin's holder will pull out their money from it. Also, even you're skilled enough in hacking, if your target is also smart and his account his secured, your time will just be wasted. Bitcoin was designed for the security of transaction. It has a capability to keep the transaction anonimously, hence the accounts's identity is impossible to determine.