Online playable strategic multiplayer games
 

My question is what strategic games are playable online without an CD/DVD and the correct serial number? (Like Call of Duty 2 but strategic!)

What is the problem with the need of a correct serial number.
If you want to play a game, then you have to buy it. If you buy it, you'll have a correct serial number.

(Read the BOARD RULES carefully before you post an answer.)