Hopefully I addressed it in the section above.

I believe that intelligence agencies are targeted all the time, and keeping machines clean is not that easy. Certain governments (like Singapore) adopted an air-gap approach, so the machines you use for work don't touch the internet.

But even then, it would be a lot easier to infect that persons's home machine.....Many of the people visiting Guccifers site were normal people, some were from intelligence agencies (proportionally probably a lot more than visit a normal site).

Assuming you had AWESOME undetectable malware, you'd have to infect the lot, get them to report in, and ferret out the interesting ones. Not exactly a weekend project, but if this was your passion in life, very achievable.

Spear phishing these guys is hard, watering hole may be easier.