Possible Duplicate:
XKCD #936: Short complex password, or long dictionary passphrase?

How are long passwords more secure? The only situation in which I can accept long passwords are more secure is when someone is literally standing behind you, seeing what you are typing.

When it comes to someone using a Keylogger or Sniffer, the password length doesn't matters at all, your password will get compromised no matter what. Yet, at a lot of places I read/hear that long passwords are more secure. How?

Can someone mention some other situations in which long password will not get compromised whereas smaller will?