Xfce4-screensaver license issue.
If you have read Slashdot, if not, please do it now. Lots of years ago GNOME developers copied code from Xscreensaver (BSD license), released it as GPLv2 and removed the authorship of Jamie Zawinski. Therefore [cinnamon/mate/xfce4]-screensaver and several more projects forked from gnome-screensaver violate Xscreensaver license and Zawinski's copyright. Basically every OS distributing [gnome/cinnamon/mate/xfce4]-screensaver are shipping [copyright/license]-infringing code.