"...if these people can hack encrypted files , is on line banking next?"
Online banking security is a lot more robust than Twitter, but in theory anything can be hacked. Banks use some sophisticated methods of security enhancement - mine, for instance, knows if I use anything other than my laptop to try to access my account, and it asks me to provide the answers to two additional security questions before it allows me to use my username/password/security code combination.
Banks accounts have been hacked, but it's a rare occurrence, and if it happens your bank should make good any losses - provided you can satisfy it that you took adequate steps to protect your login details.
It goes without saying that you should never, ever, under any circumstances allow these to be stored on your computer. If you use a public access computer - in an airport or hotel, for instance always go into the browser settings when you've finished, and delete the history. I also clear the cookie cache, but it's best never to use public access machines if you can avoid it.