Breaking into the unclassified internal network, Russian hackers have disrupted computer operations at the White House.

The White House is under constant assault, but this attack is more serious because of both its intensity and persistance. Reports are that the attack has been going on for the last three weeks.

White House officials say that the attack has not breached classified systems.

One White House official, speaking under condition of anonymity, said: “In the course of assessing recent threats, we identified activity of concern on the unclassified Executive Office of the President network. We took immediate measures to evaluate and mitigate the activity … Unfortunately, some of that resulted in the disruption of regular services to users."

The memo from the White House says: "Our computers and systems have not been damaged, though some elements of the unclassified network have been affected. The temporary outages and loss of connectivity that users have been experiencing is solely the result of measures we have taken to defend our networks."

Attribution of attacks in cyberspace is difficult. It's well known that Russian hackers are among the most capable on the intelligence scene so the unproven attack is very plausible. Security firms FireEye and Trend Micro have blamed hackers affiliated with the Kremlin with attacks against targets including NATO, the Ukrainian government and US defense contractors.