1. An automatic lexicon generation system to identify and construct a list of English phrases from a user specified set of example e-mails and documents written in English, said phrases being a set of relevant key phrases useful for identifying information leak in an archive of e-mails, said system comprises: a) means ( 102 ) to identify a set of important key phrases from a user specified set of example e-mails leaking information and documents leaking information, written in English, using frequency analysis, word stemming, and removal of common words and domain specific words ( FIG. 1 , FIG. 4 ); b) means ( 102 , 506 , 511 ) to identify a set of important key phrases from a user specified set of example e-mails not leaking information and documents not leaking information, written in English, using frequency analysis, word stemming, and removal of common words ( FIG. 1 , FIG. 5 ); c) means ( 405 , 511 ) to identify a set of relevant phrases and to assign a label, one of “very highly sensitive”, “highly sensitive”, “sensitive”, “not sensitive” or “sensitive” to each of the phrases of said set ( FIG. 4 , FIG. 5 ); (d) means ( 613 ) for assigning weights to each of said key phrases ( FIG. 6 ); e) means ( 614 ) for building multiple key phrase lists and weights from said important key phrases ( FIG. 6 ); f) means ( 615 ) for presenting said lists of key phrases to the user for simulation and for storing the final approved list as weighted category lexicon ( FIG. 6 ) g) means ( 716 , 717 ) for using said list of phrases on an archive of e-mails and documents written in English for identifying any e-mail leaking information ( FIG. 7 ).