Why does the security code reset after restoring factory settings on my Nokia device (S40 phones)?
This is a feature. First time when you activate the security keyguard, you are asked to choose a code. This code will then be active. However, after restoring factory settings, the security code is set undefined or reset to 12345. To set the code again or change the code, select Menu > Settings > Security > Access codes > Create security code or Change security code.
