The new mega patch for A2, A2 Free and OA has been officially released in the meantime!
Be sure to check out the blog entry about v2 signatures and MP security in general.
ARMA 2 Free - Combined Ops Lite
Recently basic game-distribution support was added to Six Updater, currently you can download ARMA 2 Free from the Games section of the software.
Be sure to get your free key from the Activation site.
ARMA 2 Free can be played online, or used to combine with OA (Operation Arrowhead) / RFT (Reinforcements) to get ARMA 2 Combined Ops lite!
You'll still lack the ARMA 2 original campaign and missions, and have some reduced texture quality, but you can join any Combined Ops server successfully.
This configuration is automatically supported in Six Updater if you install ARMA 2 Free!