Blockage of 12 Out Of 13 PLC Systems

Event Year: 2004 Reliability: Confirmed
Country: Switzerland
Industry Type: Other

Two out of the 13 PLCs of the control system for the plant lost communications, with 10 PLCs more following in the next 30 minutes after the start of the incident. The corresponding modules (Siemens CP443-1 IT) were completely blocked, such that only a power-cycle was able to restart them. Since then, drop-outs of the same kind occur with a frequency of one PLC per week on average.

Suspected sources for this incident have been network broadcasts or network scans, but no proof has been found in susequent network sniffing.


The loss of a PLC inhibits the proper functioning of the facility. In worst cases, this can lead to production losses of up to 8 hours per incident, depending on the status of the process.

Action Description: The future plans are to put the whole system on a dedicated (virtual?) network. This move has not been accomplished at the time of this entry.