The NSA, the original primary developer of SELinux, released the first version to the open source development community under the GNU GPL on December 22, 2000.[6] The software was merged into the mainline Linux kernel 2.6.0-test3, released on 8 August 2003. Other significant contributors include Red Hat, Network Associates, Secure Computing Corporation, Tresys Technology, and Trusted Computer Solutions.
We saw a very sophisticated attack on Linux earlier this year with the XZ exploit. That stuff is terrifying and the sort of thing people should be worried about. SELinux is tame, by comparison.