Three German security researchers have presented a PLC-based worm with Proof-of-Concept based on the Siemens SIMATIC S7-1200 PLC. The worm was designed and developed specially for the PLC environment, which resulted in a custom and optimized PLC worm. Worm takes into account computing limits of PLCs and uses the limited resources accordingly. Worm replicates itself on the target PLC using ports and protocols used by Siemens. It can also start an endless loop which will eventually cause PLC to crash in a denial of service attack.”]
Source: https://securityaffairs.co/wordpress/47045/hacking/armageddon-plc-based-worm.html