For the bugging and resetting, you can take precautions and use fallback saves to prevent a complete reset. If you are cautious, this shouldn't be too much of an issue.
The problem with saving progress would be, that banks are stored client-side, so everyone has access to their own save files. Given enough time and dedication, people will eventually find out, how to modify them to their benefit, regardless of all precautions you take. All you can do is make it hard for them. You can (and should) encrypt the information stored in the bank, you can verify the bank with a signature (which, in theory, should be enough to secure the bank, this has proven to be easily circumvented, though).
However, you need to also keep in mind, that everyone has access to your map in the editor, map protection is ineffective and can be negated in seconds. So all kinds of obfuscations etc can be figured out, just by looking at your code. Of course, you can obfuscate your map script, as well, but again, this is no life saver, but merely additional effort for a potential bank hacker.
So unless Blizzard changes something, like storing banks server-side or whatever, you will never have 100% secure banks. But the effort might be too big for people to bother.
However, if some people can crack it and there is a high demand for it, they could just create a program, so everyone could easily do it.
Yes, this might very well be the case ;)
For the bugging and resetting, you can take precautions and use fallback saves to prevent a complete reset. If you are cautious, this shouldn't be too much of an issue.
The problem with saving progress would be, that banks are stored client-side, so everyone has access to their own save files. Given enough time and dedication, people will eventually find out, how to modify them to their benefit, regardless of all precautions you take. All you can do is make it hard for them. You can (and should) encrypt the information stored in the bank, you can verify the bank with a signature (which, in theory, should be enough to secure the bank, this has proven to be easily circumvented, though).
However, you need to also keep in mind, that everyone has access to your map in the editor, map protection is ineffective and can be negated in seconds. So all kinds of obfuscations etc can be figured out, just by looking at your code. Of course, you can obfuscate your map script, as well, but again, this is no life saver, but merely additional effort for a potential bank hacker.
So unless Blizzard changes something, like storing banks server-side or whatever, you will never have 100% secure banks. But the effort might be too big for people to bother.