infiltrate
     v 1: cause (a liquid) to enter by penetrating the interstices
     2: enter a group or organization in order to spy on the
        members; "The student organization was infiltrated by a
        traitor" [syn: {penetrate}]
     3: pass into or through by filtering or permeating; "the
        substance infiltrated the material"
     4: pass through an enemy-line; in a military conflict [syn: {pass
        through}]
Source: WordNet® 2.0