I got slightly suspicious when one of my new cards arrived 3 months before the old one ran out and I ended up going into the bank to check it was legit. As said, I can't think of anyway a bogus card can be used to put your back account in direct danger. From what I have read, people have been sent bogus cards but the scam involved the perpetrator visiting and persuading the owner to part with his old card on the pretext that this was needed to be done to allow them to sort out why the new (bogus) card was not working.