27.6.6 Security Bit
The security bit allows the entire chip to be locked from external access for code security. The security bit can be written by a dedicated command, Set Security Bit (SSB). Once set, the only way to clear the security bit is through a debugger Chip Erase command. After issuing the SSB command, the PROGE error bit can be checked.
In order to increase the security level it is recommended to enable the internal BODVDD when the security bit is set.