A sniffer can read every keystroke sent out from your machine, including passwords. But a large portion of the blame falls on the users themselves. They willingly share their passwords. More important, users are too predictable in their choice of passwords. Left to their own devices, users often choose a password that is too short or too easy to guess.
Passwords are about identity.
We tend to reveal ourselves in our passwords. Or we are wise enough to avoid any personal references but choose a word that is ridiculously short, a dictionary word, a name or word spelled backward, or an alphabet or keyboard sequence. Just because we think a foreign word is obscure doesn't mean that it isn't in a dictionary somewhere. The point is that all of these types of words are easily guessed, which makes the job of password cracking straightforward. U-M system administrators are now using some sophisticated programs that help users avoid choosing an insecure password.