Russia is the leading suspect in a sophisticated cyberattack on the unclassified email network of the U.S. military's Joint Staff that prompted the Pentagon last month to restrict access to portions of that network, U.S. officials said on Thursday.
Early reports firmly linked Russia to the attack, said one U.S. official, who declined to be named since the investigation is still underway.
"It was a spearphishing attack traced to that country," said the official, when asked about Russia's possible involvement. Spearphishing emails purport to be from colleagues.