If I lock my screen by pressing my system's "suspend" button and walk away anyone can get and photograph a glimpse of my unlocked screen just by pressing any key:
- the system wakes up and shows the contents of the theoretically-locked screen
- keyboard input is activated allowing - if one is quick - to enter and execute a command.
- the screen is locked. Alas! too late.
For Android and the iPhone more harmless ways to get glympses of the unlocked system were treated as security scandals by heise.de and golem.de (IT-centered german press services) => reporting this as a security bug.
ProblemType: Bug
DistroRelease: Ubuntu 18.10
Package: gnome-screensaver 3.6.1-8ubuntu3
Uname: Linux 4.18.1-041801-lowlatency x86_64
ApportVersion: 2.20.10-0ubuntu13
Architecture: amd64
Date: Mon Oct 29 07:54:36 2018
SourcePackage: gnome-screensaver
UpgradeStatus: No upgrade log present (probably fresh install)
Which desktop environment are you running? Are you sure you're running gnome-screensaver?