French aircraft carrier Charles de Gaulle tracked via Strava activity in OPSEC failure
(securityaffairs.com)
I remember working in military intelligence, and the number of people who couldn't understand why they couldn't keep track of their steps with a fit bit while on duty was disheartening. Opsec has been nearly dead for a decade plus at this point.
I also remember one mission where I started tracking Isis local leaders just using open information because they were playing Pokemon Go in Iraq.