I guess if the NSA hackers would really decide to crack down on Bitcoin they would manage it. Don't forget that most computers in the world are likely to have backdoors that they could exploit...
bitcoin itself cannot be hack rather the bitcoin wallets or exchanges can be but they may still struggle to do it as it really secure rather hackers only do another way such as making a phising site or a clone site that is really identical to another site in order for them to possibly steal the info or password of their victim . Other method is by creating a malware or a kind of bad software so that they can easily infect it to a downloader of their file.