Are Humvee windows bulletproof?

For those who played the closed beta:

​Are the Humvee windows actually bulletproof?

​If so, what calibers can they stop?

​Do their defense or durability degrade after taking hits?

I'm really curious about this because it might give us a good idea of how armor mechanics work on lightly armored vehicles in general. For instance, can a .50 cal sniper penetrate the doors and glass to kill crew members directly, or do lightly armored vehicles just rely on a standard health pool without actual penetration and crew damage mechanics?