Miller was named principal deputy administrator of the NNSA in 2010 and has become the acting administrator following the departure of the previous one this January. The NNSA is part of the U.S. Department of Energy, and - among other things - maintains the country's stockpile of nuclear weapons.
Guccifer has managed to compromise Miller's Facebook account and one of her personal email accounts, both of which accordingly to an official statement released by the NNSA, did not contain any classified information.
To prove the successful compromise, the hacker apparently sent to The Smoking Gun screenshots he made while inside the accounts, as well as a number of photos of her during a White House meeting. There is no word on how the hacker managed to access the accounts, and he didn't reveal his methods.
In the last half year, Guccifer has successfully targeted private accounts of Bush family members and Christopher Kojm, chairman of the U.S. National Intelligence Council (NIC).