From Newsgroup: comp.os.linux.networking

Handy intro <https://www.zdnet.com/article/this-handy-linux-tool-snitches-on-sneaky-apps-heres-why-and-how-its-helpful/>
to OpenSnitch, which can monitor and selectively block network access
by particular apps.

Just one caveat: I would recommend ignoring his advice to download and
install .deb files. Ubuntu already has its own packages available in
the standard repos, just like parent Debian, and no doubt other
popular distros as well. Stick to those instead.
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