The magnitude of this ongoing attack is hard to overstate.

The Russians have had access to a considerable number of important and sensitive networks for six to nine months. The Russian S.V.R. will surely have used its access to further exploit and gain administrative control over the networks it considered priority targets. For those targets, the hackers will have long ago moved past their entry point, covered their tracks and gained what experts call “persistent access,” meaning the ability to infiltrate and control networks in a way that is hard to detect or remove.

While the Russians did not have the time to gain complete control over every network they hacked, they most certainly did gain it over hundreds of them. It will take years to know for certain which networks the Russians control and which ones they just occupy…

The remediation effort alone will be staggering. It will require the segregated replacement of entire enclaves of computers, network hardware and servers across vast federal and corporate networks. Somehow, the nation’s sensitive networks have to remain operational despite unknown levels of Russian access and control. A “do over” is mandatory and entire new networks need to be built — and isolated from compromised networks.