|Encoding mistake makes the text illegible|
This usually happens basically because the banking software uses an older non-Unicode standard for encoding text.
The solution is very simple. You just need to change one easy setting to tell your computer that unspecified text is Korean, not English. Don't worry, this won't mess up your computer and change everything into Korean. 99% of English software will have the correct specifications to display in English. You're only changing how your computer handles texts that is explicitly missing any specific encoding info, which in this day and age is pretty much limited to Korean banks.
(on Windows 10, just click/press the Start menu and type "region", or go to the Control Panels)
Step 2: Click over to the "Administrative" tab
Step 3: Click that second box, "Change system locale..."
Mac users, I don't know. Find something similar in your settings. Just buy a real computer already, geesh.
For some background, if you're seeing that kind of jumbled text, then chances are, you likely have your computer's language set to English. In that case, your computer is assuming that any text that doesn't specifically identify what language it's in must be English, which of course in this case is wrong. This is why a Korean speaker would likely never encounter this problem: their computer is set to Korean anyway, and is presuming all text is Korean, which of course in this case it is.
This is also usually the problem when a Korean subtitle file doesn't work right in your movie player, showing the same kind of gibberish, but your Korean girlfriend's laptop works fine. If that's you, check out my short post on Korean subtitles.