Debian
Since updates to Debian software packages between official releases do not contain new features, some choose to use the testing and unstable distributions for their newer packages. However, these distributions are less tested than stable, and unstable does not receive timely security updates.  In particular, incautious upgrades to working unstable packages can sometimes seriously break software functionality. Since September 9, 2005  the testing distributions security updates have been provided by the testing security team.