[hardy263]

It's not incorrect. At the bottom of the blog post, they explore different ways to "trick" people trying to look at the fingerprints

If that weren’t enough, my friend actually brainstormed a couple of other ways to improve the password.

like using three digits but tapping a phantom fourth number once the code is entered…. so there are four “tap prints” but only three which are relevant!

[corin_]

But that's still using three unique digits. 1123 uses only three digits, but that doesn't make it a three-digit number, it's still a four-digit number.

[tobtoh]

You're right Corin - the title is a little misleading with hindsight. However, I was trying to reflect the angle that made the page interesting (ie that it's counter-intuitive that using less unique digits is more secure) whilst still trying to fit it within character limits.

[corin_]

If you are still able to edit the title (can't remember when HN stops letting you do that), a more suitible one might be something along the lines of "iPhone 4-digit passcodes more secure when containing only 3 unique digits".

[tobtoh]

Done - thanks for the suggestion Corin!