cy ‧ ber ‧ ter ‧ ror ‧ ist /ˈsaɪbəˌterərəst, ˈsaɪbəˌterərɪst $ -bər-/ BrE AmE noun [countable]
someone who uses the Internet to damage computer systems, especially for political purposes:
Such a strategic attack, mounted by cyberterrorists, would shut down everything from power stations to air traffic control centres.
—cyberterrorism noun [uncountable]