27
Never forget that Picard's PIN is 0000
(dubvee.org)
Alt text: Admiral Picard initiating the self-destruct sequence of the Stargazer by the vocal command, “Authorization: Picard, zero-zero-zero-destruct-zero”
Yeah, you can't brute force that.
You can imagine the Romulans thinking that 0000 is just too stupid to pick for a PIN, so never tried it. When they find out, they'll be kicking themselves and wondering why the Federation is a formidable opponent.