In 2008, the Idaho National Laboratory was working on the Siemens PLC and even made a presentation about it: http://graphics8.nytimes.com/packages/pdf/science/N

In 2008, the Idaho National Laboratory was working on the Siemens PLC and even made a presentation about it: http://graphics8.nytimes.com/packages/pdf/science/NSTB.pdf http://graphics8.nytimes.com/packages/pdf/science/NSTB.pdf (Page 59 and Page 60 are quite interesting as they use the security test case "Infiltrate PCS 7 ES and modify configuration").