Imagine you had a 24 word seed and had posted it somewhere where a hacker were able to find it. Potentially you were burgled and they found / took it. However, when you setup your Cold Wallet you set an additional 25th word (Passphrase)..
Would a hacker be able to tell that they had the correct 24 words and therefore know they just had to crack the 25th ? Or would they have no way to tell whether 24 words were correct or that a 25th had been used ?