Unfortunately for Newag, other than in the court of public opinion, firmware deliveries count as written evidence.
"No hacker can tell, based on the content of the digital record alone, who is the author of the digital record in question"
Boy oh boy. Either they're not singing their firmware (which is a serious indictment in and of itself) or proving that it was them all along will be trivial, but the ones signing off this message are unaware of this.
Overall they got caught with their pants down and handling it badly as evidenced by the fact that they don't even have a scapegoat prepared.
I have no idea how those systems work and what guarantees they provide, but this would be hair-raising...