This is going to affect multiplayer in our games that use Gamespy for matchmaking, cd keys authentification and NAT traversal from Arma: Resistance to Arma 3. We are planning to introduce an alternative solution using Steam to Arma 2: Operation Arrowhead and Arma 3 users.
Other games (Take On Helicopters, Arma 2, Arma 2: Free, Arma, Arma: Cold War Assault) will have more limited multiplayer experience with loss of server browser, cd key authentification and NAT traversal systems. That said, direct IP connection to servers should work even after Gamespy services are no longer available.
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