There is a bit of confusion about anti-virus software, firewalls and online banking.
Neither of them will help if
we have allowed the malware onto our computers by, for example, downloading software from sites where other apps are bundled with the one we actually want. If we do not decline these "offers" we are asking for trouble. We should also scan the download manually with our AV before running the installer; and we should never run an installer from the Internet.
Another trick to get malware is to open links in emails, even when we think we know who they are from. There are plenty of those 'You have won.....!" or "Free xyz when you....!". Avoid them like the plague.
Yes a good AV software helps, but it is always playing catch-up.
A simple extra layer of protection for online banking is
Trusteer It is from IBM working in conjunction with many banks and works to protect end-to-end communications. Most UK banks offer it on their websites, but for some reason you have to find it, and if you do not know what it is then you will probably pass on by.