UPSs are, of course, designed to provide backup power, but when staff at the company's Berlin Mahlsdorf center were upgrading the UPS they suddenly found the center without electricity.

The result was a catastrophic failure of DB's Web pages, which returned `404' messages to internet users. Meanwhile all the country's electronic and self-service ticketing machines went offline, as did station boards across Germany.

Embarrassed DB officials told reporters that they did have back-up systems in place, but these failed to trigger... due to the lack of power in the centre.

The company is "taking steps" to ensure the systems failure, which lasted several hours, will not happen again.