It was a coordinated attack using multiple zero-day exploits (holes in code not yet known by the target). You have to pay tons of money or infiltrate security firms to get such info.
A nation-state with vast resources will eventually break into ANY system as long as a data link to the internet exists. And even without a link to the internet, there are more than enough spies to infiltrate isolated networks.
So what do we do? It’s not like we can go back to the days of paper files...
>>So what do we do?
Well, not letting Termites like Eddy Thnowden and Bwadley Manning into the woodwork might be a start. Who vetted those two - and how many other treasonous pinktard punks are still operating undetected?
Our next step will be to store only encrypted data bases that use a scrambling technique to segment the data when stored. That means that you can copy a certain file but it will be disconnected garbage.