The Mobile Flak (Sometimes known as "Flak", "Flak Truck", "Flak track"), is fast, weakly armored vehicle. It is very effective against aircraft, and is the soviets' primary mobile anti air unit. However, it can also be very useful against infantry.
Although strong against aerial vehicles, it is weakly armored, and a hind or a Yak can destroy a single flak truck while still retaining some of its health. However, a small group of flak trucks (2-4) can easily destroy multiple aircraft with minimal harm.
When microed correctly, the flak truck can be invincible against infantry. It has a slightly longer shooting and sight range than riflemen and rocket soldiers and can shoot without being shot at. However, the units can easily get closer unless the player is actively controlling the flak unit. When in the range of rocket soldier fire, the flak truck is easily destroyed.
A popular tactic is applying the Iron Curtain to mobile flaks. They can then quickly infiltrate defenses unharmed, and destroy weakly armored units such as artillery and V2 rockets. There is no way to protect these units from such an attack. The best solution is taking a preventive measure and destroying an opponent's Iron Curtain, or the Soviet Tech Center prior to them building the curtain.