This is a very strong argument for FOSS to pick up the good habit of ditching/un-mainlining projects where they are sitting around for state actors to volunteer injecting commits to, and dep-stripping active projects from this cruft.
Who wants to maintain on a shitty compression format? Someone who is dephunting, it turns out.
Okay so your pirate-torrent person needs liblzma.so Offer it in the scary/oldware section of the package library that you need to hunt down the instructions to turn on. Let the users see that it's marked as obsolete, enterprises will see that it should go on the banlist.
At the same time, XZ became a cornerstone of major Linxus distributions, being systemd dependency and loaded, in particular, as part of sshd. What could go wrong?
In hindsight, the commercial idea of Red Hat, utilizing the free work of thousands of developers working "just for fun", turned out to be not so brilliant.
A lot of comments in this thread seem to be missing the forest for the trees: this was a multiyear long operation that targeted a vulnerable developer of a heavily-used project.
This was not the work of some lone wolf. The amount of expertise needed and the amount of research and coordination needed to execute this required hundreds of man-hours. The culprits likely had a project manager....
Someone had to stalk out OSS developers to find out who was vulnerable (the xz maintainer had publicly disclosed burnout/mental health issues); then the elaborate trap was set.
The few usernames visible on GitHub are like pulling a stubborn weed that pops up in the yard... until you start pulling on it you don't realize the extensive reality lying beneath the surface.
The implied goal here was to add a backdoor into production Debian and Red Hat EL. Something that would take years to execute. This was NOT the work of one person.