The Paper Vaults that The Bank of Bitcoin allows its Members to create CANNOT be hacked. They are literally just as secure as any paper wallet.
to combat the possibility of the injection of malicious code into the client-side javascript used to manipulate your Paper Vaults we have described a two- or three-minute method to check that our code has not been altered (either by a hacker or otherwise).
One has to spend those 2-3 minutes EVERY TIME they log on. Since you know the IP and time of page loads, and when the next transaction is sent to you from that IP, you can tell who hasn't been checking hashes and how many coins those poor careless souls have in their wallets.