Implanted brain-computer interfaces would bring digital insecurity to people's brains.

The necessary starting point for Computer security is free software. Security for brain-computer interfaces requires insisting that the software that controls the interface be free. This includes not only the firmware in the device itself, but also other software that will tell the firmware how to influence your brain.

For the paper referenced there, see http://sci-hub.cc/downloads/ef93/pycroft2016.pdf.