Mastercode by Mad Scientist Usage: Reset Nokia Security Code So you don't know or you have forgotten your Nokia Security code? Don't worry the solution lies in this very page! No data cable needed with this new solution. So what is a master code I hear you ask. Well lets assume you have forgotten your security code. The master code is a 10 digit number that will always be accepted as if it were your actual security code. You can then use the master code to change your security code back to what ever you like. When your Nokia handset asks you for the security code simply enter the master code. How do you generate the master code? The master code is specific to your handset and is generated using the handset 15 digit IMEI number (serial number). Just click on picture to download.