Fantastic question, like Will_a said, I’ve never seen a device designed for input to the brain like this.

In this particular example, if someone were to compromise the device, even though it’s not able to “fry” their brain with direct electricity, they could overload the input neurons with a ton of stimulus. This would likely break the device because the input neurons would die, and it could possibly cause the user to have a seizure depending on how connected the input was to the users brain.

That does bring to mind devices like the one developed by Battelle, where the device reads brain activity and then outputs to a sleeve or cuff designed to stimulate muscles. The goal of the device is to act as a prosthesis for people with spinal cord injuries. I imagine that device was not connected to the internet in any way, but worst case scenario and a hacker compromises the device, they could cause someone’s muscle to sieze up.