Man In The Middle

A Man In The Middle (MITM) attack is a sophisticated attack where a fraudster hijacks a link from a user to a known web service such as retail banking web site.  The fraudster relays information from the user to the web service and from the web service back to the user in such a manner that neither side knows that anything is wrong.

Man-In-The-Middle attacks successfully thwart One Time Passwords such as are generated by hardware tokens (eg SecureID).  MITM attacks are very popular now because it's very straightforward to attack the Domain Name System at a number of points including home wireless routers and the DNS protocol in general.