[ok123456]

Back when people customized screensavers, you would put the .scr file (a regular exe) in the Windows directory, and it would populate the list of screen savers? I'm guessing that's no longer a thing in the name of security theater.

[ndsipa_pomu]

Not so much security theater as a large number of exploits were disguised as .scr files as it was easy to trick a user into downloading one and then it would run with full system access

[ok123456]

Restrict .scr to run as an unprivileged user without network or filesystem access, that always launches the system login/unlock on exit?

This seems better than having a program that does random web requests to put ads on the lock screen.