In the 90s, MIT's Athena system devised a system to handle online harrassment. One feature of the system was that the notice of reported abusive behaviour sent to the accused user began with the phrase "Someone using your account…". Users were advised to re-password their accounts, as they may have been hacked. Password resets by UYA recipients were taken in good faith by staff, but the most astonishing thing was that the offending behaviour nearly always stopped there.
https://www.metafilter.com/173881/UYA-notices-and-face-saving-in-moderation-systems#inline-7389802
I need to remember this technique in the event of anyone doing stuff that merits a warning.