Something in their implementation of SMART or some other chip on the controller? No idea what exactly it would have been a backdoor too. The OS? The BIOS? The

Something in their implementation of SMART or some other chip on the controller? No idea what exactly it would have been a backdoor too. The OS? The BIOS? The data on the drive? Memory? Toshiba has offered a number of hardware and software encryption options over the years, but a casual search didn't turn up much older than 10 years.