These are good questions to ask. The right thing for you to do is study how a computer intrusion campaign works and how attribution is done. Everyone has thei

These are good questions to ask. The right thing for you to do is study how a computer intrusion campaign works and how attribution is done. Everyone has their own limit of when they trust expert advice. For example, I refuse to trust my doctor's advice fully and pull up studies at home to verify what she tells me. It's good to learn more about computer security if it interests you. It is extremely difficult, maybe impossible, to completely conceal one's pivots, implants, and exfiltration in a computer network. True, it is possible that an attacker that is more capable than GRU/Cozy Bear and FSB/Fancy Bear did just that and exfiltrated the emails and documents. But this is going beyond what the evidence suggests.