[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!