[tux3]

Malware that's already on your system can do whatever it wants. NAT punching is not some complicated dark art for people who already have working exploits...

[GekkePrutser]

No but it stops them using your system as a C&C node accepting connections from external systems.

It doesn't stop it per se but it makes it a lot harder. Part of security is not being the easiest target on the block.