A few years back a company I was contracting for had one of their end users report a high severity security defect. Apparently he signed into the app and thought he had been hacked because a couple of large 6-figure transactions had been made.
After several hours of inconclusive investigation where even identifying the user proved difficult, this turned out to be him seeing the marketing example screens in the app store and having a panic. The app never even got installed and he never signed up for it.
The marketing screens were quickly updated to show something less impressive and with a sample data only warning...