Can you explain a little bit more do you mean that you cannot finance with your bank with windows 8.1 ??
Could be a problem of IE11> Many banks using IE for Internet Banking and They for sure didn't updated yet to IE11!
I have just tested here in Norway, and my Nordea bank is not supporting Internet Explorer 11 yet. I'm using Firefox and it's works great. Remember that Windows 8.1 is not public available before in about one month, so I'm sure all the banks has fixed the issue by then.
Solution to this problem. IE 11 seems to not be able to detect if website requires compatibility mode or not. you needed to do it manually, press the Tool icon at the top right and select compatibility mode and add your site to the list. to do this right click IE anywhere on the top bar and click menu then click tools and look for Compatibility Mode Settings. Then manually enter the site that is not working correctly. I think its a bug in IE11...
TBH I find it a bit careless to use IE11 for banking already.... Banking is one of the most sensitive actions one can make online. IMHO only reliable browsers which are already proved to be successful should be used.
Some of the big banks in Thailand accepting IE for Internet Banking only! There's no other choice, like it or not!
Perhaps "appropriate security settings" means disconnecting the network cable, in which case all browsers are equally secure.