Nurgak
Setting a higher security in lock fuse bits doesn't allow to set a lower security value without a complete memory wipe (which resets them automatically), so setting programming fuses before programming isn't necessary (the `if (!target_progfuses())` on line 148), unless other fuses change apart from the lock fuse. But the actual problem is the writing of the lock bits: you're sending `0xAC`, `0xE0`, `0x00` and then the lock fuse, but the datasheet says that when writing the lock bits the 2 most significant bits of the sent data should be 1, this is quite dangerous as it doesn't write the right lock bits. The fix is on line 519: Replace: `Serial.print(spi_transaction(0xAC, 0xE0, 0x00, f), HEX);` With: `Serial.print(spi_transaction(0xAC, 0xE0, 0x00, 0xFF & f), HEX);`