In the post-Stuxnet cyber security world, many vendors are actively thinking about protective measures that could prevent a similar attack on industrial systems.
Such measures could be implemented at the PC-level, the PLC-level, or even the Profibus or device-level. They could include methods such as antivirus-scanners, firewalls, patch management, password policies, USB usage policies, code integrity checkers, etc. However, all of these measures are ones that are implemented at the highest levels of an industrial system.