Boffins hacked Siemens Simatic S7, most secure controllers in the industry August 11, 2019 https://securityaffairs.co/wordpress/89720/hacking/siemens-simatic-s7-hack.html Research paper: "Rogue7: Rogue Engineering-Station attacks on S7 Simatic PLCs" (PDF - 583 KB): https://i.blackhat.com/USA-19/Thursday/us-19-Bitan-Rogue7-Rogue-Engineering-Station-Attacks-On-S7-Simatic-PLCs-wp.pdf
Nothing is unbypassable if a researcher has time to work on it. it is like a lock on your door, you just delay the housebreaker based on the lock sophistication but if he has all the time he needs, he will manage to enter. so im amused by the naivety of some vendors claiming they never found their soft bypassed, it was, is and will but they dont know it yet, just give someone the motivation to do it.