I'm unaware of any successful hacking attempts made against Armory. The only possibility I can think of would be one where somebody has an unencrypted wallet that gets copied when somebody has physical or remote access to the computer. The solution in that case is quite simple: Encrypt your wallets with a passphrase.
You should never have an unencrypted wallet without very specific reasons, and an unencrypted wallet should never hold more coins that whatever you're willing to lose.
Or, as the last poster said, I suppose a keylogger could steal your passphrase. Not much we can do there, unfortunately. It'd be cool to add some code that understood one's typing cadence and such, and could tell if somebody wasn't you. I'm not going to write that code! (Hell, short of hiring a real expert in that particular field to write it, I'd object to such code being in Armory, period.)
