Arma 2/Arma 2 Operation Arrowhead 

As I understand it Bohemia hasn´t released any sales numbers for Arma 2 and it´s standalone expansion,Operation Arrowhead,but considering that on the official site of the DayZ mod there are over 1.3 Million unique legal users,both Arma 2 and Arma 2 OA have sold at least 1.3M copies each(obviously they sold more but that´s the only metric available),so I suppose both of them can be added to the list,either by listing each at 1.3M or,just like Guild Wars,putting both together at 2.6 Millions.

Thanks.