wire tapping

from The Collaborative International Dictionary of English v.0.48

Wire tapper \Wire tapper\
   One that taps, or cuts in on, telegraph wires and intercepts
   messages; hence (Slang), a swindler who pretends to tap wires
   or otherwise intercept advance telegraphic news for betting.
   -- {Wire tapping}.
   [Webster 1913 Suppl.]