[ghelmer]

I'm not apologizing for MS, and I have no idea what PII protection Recall actually has. If Recall does have real PII logic, it should recognize that a legitimate VISA payment card numbers must start with '4' + be 16 digits in length, and AmEx cards must start with '34' or '37' + be 15 digits in length; also, the LUHN algorithm must be satisfied over the card digits.

With Recall, it seems false positives for PII-type protection rules would be more acceptable than false negatives. But with the negative press already around the technology. I'm not sure it will ever gain acceptance.

[Rygian]

Folks at $dayJob keep a list of prefixes of credit card numbers that don't satisfy Luhn, currently there's 8 of them.

And while we're at it, length of credit card numbers is not fixed, can go from 12 to 19 numbers (both Luhn and non-Luhn).

[Rygian]

There are card numbers that don't satisfy Luhn.

[drdaeman]

I'm really curious now - which cards don't conform?

I always thought it's basically an industry standard and no network issues cards that don't have a correct checksum.

[ceejayoz]

https://stackoverflow.com/questions/7863058/does-the-luhn-al... has a list.

[drdaeman]

Wow, thank you. TIL!

[exikyut]

TIL, although this isn't a field I need perfect knowledge of.

I wonder if people with such cards have inexplicable problems with certain payment systems?

Edit: just saw the sibling comment, was viewing an old copy of the page