You still legally require your original 26-character Warcraft 3: Reign of Chaos and Warcraft 3: The Frozen Throne CD keys to install the game.

While exact patch notes varied by minor subversions, common elements associated with the 1.31 update series include:

Unlike older patches (like 1.26 or 1.27), version 1.31 runs natively on 64-bit modern Windows operating systems with updated graphics API support, resulting in smoother frame rates.