Swiss-cheese security

Cory Doctorow's How I got scammed was a fascinating read. Phishing has gotten more sophisticated, but also, even people whose security practices are way above the norm can get hit when the stars (mis)align just so.

There's a name for this in security circles: "Swiss-cheese security." Imagine multiple slices of Swiss cheese all stacked up, the holes in one slice blocked by the slice below it. All the slices move around and every now and again, a hole opens up that goes all the way through the stack. Zap!

The fraudster who tricked me out of my credit card number had Swiss cheese security on his side. Yes, he spoofed my bank's caller ID, but that wouldn't have been enough to fool me if I hadn't been on vacation, having just used a pair of dodgy ATMs, in a hurry and distracted. If the 737 Max disaster hadn't happened that day and I'd had more time at the gate, I'd have called my bank back. If my bank didn't use a slightly crappy outsource/out-of-hours fraud center that I'd already had sub-par experiences with. If, if, if. [...]

The following Tuesday, I called my bank and spoke to their head of risk-management. I went through everything I'd figured out about the fraudsters, and she told me that credit unions across America were being hit by this scam, by fraudsters who somehow knew CU customers' phone numbers and names, and which CU they banked at. This was key: my phone number is a reasonably well-kept secret. You can get it by spending money with Equifax or another nonconsensual doxing giant, but you can't just google it or get it at any of the free services. The fact that the fraudsters knew where I banked, knew my name, and had my phone number had really caused me to let down my guard.

Years ago, I got a call on a weekend from someone claiming to be from my credit card and was just plausible enough for me to not hang up. (Also a claimed fraud alert.) But I got suspicious when the caller started asking me for private information and then claimed it was necessary to authenticate me (at my own phone number). So I said "I also need to authenticate you; what's my mother's maiden name?" Oh no, the caller said, we can't give you that information... but with all the data breaches we've seen, that technique is no longer safe. The phisher might have my mother's maiden name [1]. Doctorow's phisher had his unpublished phone number. Secrets aren't.

[1] Helpful tip: don't use the actual answers for security questions that people might be able to research or guess. As far as your bank is concerned, your mother's maiden name can be QjFVa6ufeqr_7.