Ron Rivest and Ari Juels, well-known RSA researchers, put forth the use of fake passwords called “honeywords” to “pollute” an organization’s password database, in order to help detect such attack attempts. When the attacks uses one of the fake passwords, this will alert admins that an attack is underway. Read more here:
http://www.eweek.com/security/polluting-password-files-can-make-attacks-detectable-researchers/