strict access control and version control systems, as well as an easy-to-understand programming language make it likely that unauthorized changes to programs will happen and remain unnoticed. Prior to the discovery of the Stuxnet computer worm in June 2010, the security of PLCs received little attention. Modern programmable controllers generally contain a real-time operating systems, which can be vulnerable to exploits in a similar way as desktop operating systems, like Microsoft Windows. PLCs can also be attacked by gaining control of a computer they communicate with. , these concerns have grown as networking is becoming more commonplace in the PLC environment connecting the previously separate plant floor networks and office networks. In February 2021, Rockwell Automation publicly disclosed a critical vulnerability affecting its Logix controllers family. Secret cryptographic key used to verify communication between the PLC and workstation can be extracted from Studio 5000 Logix Designer programming software and used to remotely change program code and configuration of connected controller. The vulnerability was given a severity score of 10 out of 10 on the CVSS vulnerability scale. At the time of writing, the mitigation of the vulnerability was to limit network access to affected devices. Safety PLCs Safety PLCs can be either a standalone model or a safety-rated hardware and functionality added to existing controller architectures (Allen-Bradley Guardlogix, Siemens F-series etc.). These differ from conventional PLC types by being suitable for safety-critical applications for which PLCs have traditionally been supplemented with hard-wired safety relays and areas of the memory dedicated to the safety instructions. The standard of safety level is the SIL. A safety PLC might be used to control access to a robot cell with trapped-key access, or to manage the shutdown response to an emergency stop on a conveyor production line. Such PLCs typically have a restricted regular instruction set augmented with safety-specific instructions designed to interface with emergency stops, light screens, and so forth. The flexibility that such systems offer has resulted in rapid growth of demand for these controllers. PLC compared with other control systems PLCs are well adapted to a range of automation tasks. These are typically industrial processes in manufacturing where the cost of developing and maintaining the automation system is high relative to the total cost of the automation, and where changes to the system would be expected during its operational life. PLCs contain input and output devices compatible with industrial pilot devices