Patch 3.3.3 (2010-03-23): The amount of strength granted is now 20%, up from 10%.
Patch 3.2.2 (2009-09-22): Cooldown reduced to 1 minute and changed back to granting 25% additional armor while active instead of flat damage reduction based on armor. The amount of strength granted has been reduced to 10%.
Patch 3.1.0 (14-Apr-2009): Now grants damage reduction instead of physical damage reduction. Cooldown increased to 2 minutes from 1 minute. During WotLK beta and onwards to 3.1.0, Unbreakable Armor increased the armor and parry chance instead of a fixed damage reduction.