A new hi-tech railway signalling system being tested in the United Kingdom could potentially be hacked by cyber criminals to cause oncoming trains to crash into one another at highest speeds. Internet security expert David Stupple said the new mainframe could easily expose the systems to malware and allows malicious actors (like terrorists) to cause massacre around the UK. The biggest threat of hacking could come from an insider rogue employee. Network Rail, the in charge of the new train line upgrade that is expected to be completely operational by the 2020s, confirmed it has acknowledged the threat.
Source: https://thehackernews.com/2015/04/hacking-train-crash.html