A very important topic these days.  The US Governmental has a Control Systems Security Program that posts vulnerabilities to software and hardware typically used in industrial automation.  These usually include general descriptions of the security issue and links to the vendor for more detailed information on how to implement workarounds of patches for the problem.

Eng-Tips - General engineering forums that covers all general groups of engineering.  You can find a professional from any field to ask questions to or bounce ideas off of.

PLCS.net - Web forum to learn about programmable control systems.  Many experts available across a broad range of industries to help with your problem.  I post at this site under the screen name "dash".