4
bank collects MAC addresses
(infosec.pub)
Probably a rudimentary device ban. Banks are usually pretty behind on these kinds of things, they'll follow some advice they were given 15 years ago, even if it doesnt make sense anymore.
It's a fingerprint that can be used to cross-reference and de-anonymize your online activity, either by your bank, or by the 298 unscrupulous partners who your bank has decided to share your information with. Kinda like cookies, but they don't need to ask for permission.