ALT A heatmap reveals the most common 4 digit PIN numbers, visualised from the data leaked from several large data breaches. The horizontal axis plots the frequency of the first two digits, the vertical axis the second two digits. Clear (and somewhat predictable) patterns emerge from the dataset. A diagonal line of ‘heat’ from bottom left to top right reveals people choosing double digits (2323, 6868 etc). A strong horizontal line at the 19 point shows people using their birth year as a PIN code (1971, 1998 etc). And a large amount of heat in the bottom left shows how people commonly use their birthdate in a MM/DD or DD/MM format. The most common code in the set is 1234.