Stuff like this has been happening for decades and there have been breaches of proprietary, ie Boeing and Lockheed corporate, networks, possibly even more secure DoD networks but I'd be hard pressed to believe that they have gotten anywhere near the launch codes. Inside White House Comms day-to day unclass network probably, nuke codes highly unlikely.
Also note that the attack was identified as spear pfishing and shut down before any data actually left the server Basically somebody opened an email addressed to them that had bad code and the anti-virus caught it.