Siemens SIMATIC S7-400 PN CPU devices with firmware 6 before 6.0.3 allow remote attackers to cause a denial of service (defect-mode transition and service outage) via crafted ICMP packets.
https://cert-portal.siemens.com/productcert/pdf/ssa-589272.pdf
http://www.us-cert.gov/control_systems/pdf/ICSA-12-212-02.pdf