[Kwpolska]

What security implications do you have in mind? Hiding the number is evil for the 16-digit CC number and still dumb for the expiry date and security code. Also, autocomplete for those fields is something many people want, and is a browser feature. I can’t see anything else security-related that makes any sense to have for CC numbers specifically.

[JulianMorrison]

Having them scraped, or auto memorized and dug out of cache with a tricksy autofill form, or peeked out of RAM, or I dunno... in general being treated as something other than the highly sensitive personal information they are. Financial businesses acting according to the rules of PCI DSS are not allowed to store credit card numbers or CVVs in the clear anywhere. But browsers shrug and treat them like any old text.

Graphically I was thinking of the opposite of hiding the number, but rather making it clear to see by automatic digit grouping and stuff.