1. http://www.nextgov.com/nextgov/ng_20120123_3491.php
2. The Telegraph: Cyber attack hits German train stations as hackers target Deutsche Bahn.
http://www.telegraph.co.uk/news/2017/05/13/cyber-attack-hits-german-train-stations-hackers-target-deutsche/
3. ISA 99: Standards of the Industrial Automation and Control System Security Committee of the International Society for Automation (ISA) on information security.
http://isa99.isa.org/Documents/Forms/AllItems.aspx
4. IEC 62280 Railway applications, Communication, signaling and processing systems–Safety related communication in transmission systems, September 2010 (CENELEC EN 50159)
5. IEC 62425 Railway applications, Communication, signaling and processing systems – Safety-related electronic systems for signaling, February 2003 (CENELEC EN 50129)