At the Black Hat Europe 2016 two security researchers devised undetectable attacks that could be used to hack PLC systems avoid being detected. PLC rootkit doesnt target the PLC logic code like other similar malware making hard its detection. The malware interferes with the connection between PLC runtime and logic with the I/O peripherals. Both attacks are able to bypass Intrusion Detection for Embedded Control Systems such as Autoscopy Jr. Security also presented a version of the attack that leverages shellcode.”]
Source: https://securityaffairs.co/wordpress/53069/hacking/plc-attacks.html