Blizzard has decided to sue Valve for using the Dota name which ‘for more than seven years has been used exclusively by Blizzard and its fan community, under license from Blizzard.’ according to Blizzard. Dota (or DOTA) stands for ‘Defence of the Ancients’ a fan made map for Warcraft 3. Valve hired the creator of the map and trademarked the name Dota to use for their upcoming MOBA (Multiplayer Online Battle Arena) game, Dota2.
Article has been corrected. Blizzard isn’t suing just taking legal action in opposition to Valves trademark of Dota.
The main point is still the same though, Blizzard are trying to stop Valve from using the Dota name on their game Dota 2.