Warning from history: I remember reading, many years ago, of one chap who had a super-unbreakable password which he was requested and required to use for sensitive logins (possibly NSA-sensitive). One day, he tried his magic password on a password-strength program, which said: "Bingo: that password is well-known." Turns out he'd used his super-unbreakable password on a talker, and that the talker's owner, who also happened to write the password test program, had tipped the talker's password file (kept in plain text) into the tester's list of well-known passwords.