They have been used extensiveley by terrorist actors; however not within western countries which surprises me as well.

For a quick reference on the history of drone use check
https://www.icsve.org/isis-drones-ev...istics/#_ftn44

Noteworthy:
Terrorists have tapped into unsecured camera feeds of military drones to conduct hostile surveillance.
This is still possible with many industrial grade IP-cameras and poses a problem of it's own.