<< So, what does online banking run on? >>
Whatever OSs and protocols are used, online banking runs on the Internet.
Which means that online banking is as secure as the least secure point between your computer, the internet, and the bank's computers. By whichever pathway the information travels.
Security is sacrificed in the name of convenience.
But I am not concerned.
I mean -
What could happen?
ATMs are relatively secure, but there are lapses. For example, robberies still occur: I know one gentleman - an attorney in his 40s, 5' 11", 170 pounds - who gracefully accepted a punch in the face (broke his nose) rather than punch in his ATM number during a robbery. That ATM number would have allowed access to every account he had in that bank - I suspect that the ATM machine would have run dry before completely draining his funds. He was in Budapest at the time - wearing a nice suit and a pair of Aldens.
Always dress to fit in when travelling overseas. Slightly underdressing - but not slumming - makes you a less interesting target.
Occasionally one hears of a murder - I recall one as far back as 1984 - in similar circumstances.
Checkbooks are most secure: the robber who demands a check is not long for freedom. But I have had one incident even with checks - adolescents who stole a few checks from my checkbook and cashed them. A few hundred bucks - seemed like a lot to them at the time, I suppose. Caught, with parental involvement and full restitution. Not expelled, but I understand that the headmaster taught them a powerful lesson in life. Ouch.
I learned one, as well.
You pays your money and you takes your choice.
Regards,
Epaminondas