Couple of points that are worth clarification.

The term backdoor, to me at least, describes adding a hidden feature to software code to allow you access at root level. From all accounts this is not how the offensive capability of the NSA works.

The offensive capability of the NSA and the separate group responsible for cyber-warfare relies on having the actual code of the program and looking for weaknesses that they can write targeted exploits for. Additionally the black budget outlined that they set aside money to purchase zero day exploits on the underground market for code.

Secondly anti-virus is a joke. Nothing needs to be done to hide yourself from Symantec or any other vendor that relies on heuristic scans to detect new problems. Have yet to attend a Tech-Ed security session where any of the presenters were using it, bc of its limitations. However Microsoft's EMET is a decent next generation protection tool, that some are using as it looks to stop the method of attack not the payload of the attack after the fact.

Another point to make is that the NSA does not share RAW data with other groups. No RAW data ever leaves the NSA, this has always been true since inception of organization and was done to limit the damage of moles from other intelligence groups. The Snowden leak not withstanding.

You do need encryption for your business data, but the group you need to be wary of is China and Russia. They have a long history of economic espionage for their state owned industries.

Lastly, the network component that NSA is most likely to target is your switch. Going after the core switch is the biggest bang for the buck, instead of piecemeal attacks on individual servers or components.