A polish hacker found out why trains did stop working. The manufacterer implemented a hidden electronic switch, which automatically activated after trains were serviced by a different company.
Polish train manufacturer that lost servicing tender programmed train controller to brick itself after train stays for some time in 6 ISP facilities or in 1 their faculity(for testing?) until undocumented button combination is pressed. Some controller versions brick itself after train is idle for 10 days. After news about this...