From Fedora Project Wiki
This is a personal opinion and may not represent the Fedora Project

ATrpms warning

Warning: exercise caution before using the ATrpms software repository. I do not advise using yum with it enabled.

ATrpms has in the past replaced key Core packages, including fedora-release and yum, amoung others, pointing to its own repository. These packages are named in such a way that they are installed rather than Core packages. And when such important packages are replaced it can be very difficult to remove them.

ATrpms help can be found on their mailing lists