MCI "security" is provided by a contractor called First Line, IRRC. This has been the case since Fall 2003 at least.
It really gives us the worst of both worlds, since the TSOs are much more arbitrary and make up their own rules much more frequently than the "real" TSA. Once, when I had reason to complain, First Line told me to complain to TSA, who told me to complain to First Line, and so on ad infinitum.