[beloch]

A MITM attack occurs when an eavesdropper inserts herself between two people trying to communicate securely. e.g. Alice and Bob may think they're talking to each other over an encrypted link, but they're both talking to Eve. Eve's just taking everything Alice sends, decoding it, copying it, re-encoding it, and sending it on to Bob. A MITM attack is not necessarily the result of bad encryption, but of a failure in authentication. Eve's ability to fool Alice into thinking she is actually Bob is key.

An unencrypted connection (such as plain old FTP) is effectively a broadcast. No attack, MITM or otherwise, is required. Eve just has to listen.