You hear from time to time that someone hacked some computers, encrypted their contents and asks to pay for decrypting. We decided (2017) that the best protection against it we can imagine is to disconnect our computers from internet.
We prepared (before 2017) a solution against it but there were simply no time to finish it. The idea is the USB-USB connection with our own protocol and a button at connecting device. After pressing the button the microcontroller will allow for sending only one file (our programs will be used at both PCs). It will give us certainly a better control of what is traveling between computers than when just inserting flash drive.