Ahhh, now it makes sense...
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RT @linuxjournal@twitter.com
An unauthorized version of @archlinux for #WSL is now available from the Microsoft Store. @BleepinComputer reports this version has "added an unknown repository to the pacman.conf file, so if you install packages through it, it is not known if they have been tampered with."
https://twitter.com/linuxjournal/status/1128774069216845825