man in the middle attack
n. A computer security breach in which a malicious user intercepts — and possibly alters — data traveling along a network. (Also: man-in-the-middle attack.)

Example Citation:
If it delivers what's promised, Funk's Odyssey software will let enterprises use familiar password-based authentication for wireless LANs and existing authentication databases, but protect these interactions from the special weaknesses of wireless links, such as eavesdropping or so-called "man in the middle" attacks.
—John Cox, "Funk releases 802.1x software for WLAN security," InfoWorld Daily News, February 5, 2002

Earliest Citation:
Computers operating at speeds far in excess of current ones are technically feasible. Building them is only a matter of money. The cost of $4, $10 or $50 million might be high for a university or major corporation, it's peanuts for NSA. Informed sources indicate that such a computer would be capable of cracking a Clipper cipher in a matter of minutes. Clipper also lends itself, under proper conditions, to a 'man in the middle' attack. --"How string is Clipper?," Computer Fraud & Security Bulletin, May 1, 1994 Thanks to Gareth Branwyn, Wired magazine's chief jargon watcher, for letting me know about this phrase.

This exploit also goes by the name TCP hijacking (where TCP is a method by which data is transmitted across a network).

Related Words: