The xz package has been backdoored
Update: To our knowledge the malicious code which was distributed via the release tarball never made it into the Arch Linux provided binaries, as the build script was configured to only inject the bad code in Debian/Fedora based package build environments. The news item below can therefore mostly be ignored.
We are closely monitoring the situation and will update the package and news as neccesary.
TL;DR: Upgrade your systems and container images now!