Apparently for a bigger market share (or in reality, for Russia to take a hard line stance against software pirates), MS gives them full access to the source code.

Why is this bad? People who use MS products and have to rely on the products' security do not have access to this and the ability to find subtle items that can be easily turned into zero day exploits. So the blackhats have a nice edge here, while the whitehats are fighting an uphill battle.