Oh baloney. Banking over wifi is just as secure as banking over a wired connection. All banks use https connection for connecting to them. That is different than the usual http connection. The S stands for secure.
"Hyper Text Transfer Protocol Secure (HTTPS) is the secure version of HTTP, the protocol over which data is sent between your browser and the website that you are connected to. The 'S' at the end of HTTPS stands for 'Secure'. It means all communications between your browser and the website are encrypted. HTTPS is often used to protect highly confidential online transactions like online banking and online shopping order forms.
Web browsers such as Internet Explorer, Firefox and Chrome also display a padlock icon in the address bar to visually indicate that a HTTPS connection is in effect."
I have been banking on a wifi connection for the last 15 years without issue.