From the BI forum:
Important notice: effective May 31, 2014, Gamespy will cease providing all hosted services for all games.
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.
We apologize for any inconvenience.
( http://forums.bistudio.com/showthr....2656964 )
Sounds like Arma and vanilla Arma2 face the same fate as Swat4 before. Afaik Arma3 is only available on Steam so there shouldn't be any issues. I'm not quite sure what happens to non-steam versions of Arma2: CO, but it shouldn't be too hard to integrate them into steam or patch them otherwise.