Jia Tan was the username used by a group --- probably a state intelligence agency --- on GitHub to try to attack the xz open source package. The effort aimed at trying to take over the project, and lasted for years. They managed to get a compromised package briefly into the unstable versions of some major Linux distros that created a backdoor in the openssh daemon and came close to being widely deployed across Linux servers, which would have been a very severe compromise of a huge range of systems. The account vanished when the compromise was discovered.
In February 2024, a malicious backdoor was introduced to the Linux build of the xz utility within the liblzma library in versions 5.6.0 and 5.6.1 by an account using the name "Jia Tan".