I recently, by playing around with the LAN's default PAC file and a dummy HTTP server, discovered that on a machine that says in System Settings that Proxy Auto-Discovery is turned off, the PAC file is still fetched and used by a too-large number of Microsoft/Google background auto-update services, from Windows Update to Office.

* https://mastodonapp.uk/@JdeBP/114693762493884550

I had been lucky through having done my own experimentation, decades ago, with setting up a default PAC file on the LAN and having left it in just-send-everything-directly mode, keeping it as I upgraded things on the LAN, all of these years. Because otherwise I would have been vulnerable to a third-party in the search path for years, on a machine that clearly and unequivocally, including per direct inspection of the setting in the registry, has this switched off.

* https://jdebp.uk/FGA/web-browser-auto-proxy-configuration.ht...