The two satellites, Landsat-7 and Terra AM-1, had been interfered with on four separate occasions, allowing the attackers to be in command of the satellites for two to over twelve minutes each time.
Luckily, both of the satellites are used only for observing the Earth's climate and terrain, and the hackers never actually misused their control over them in any way. But the compromises have definitely been taken very seriously, since future targets could include satellites with more sensitive functions, such as those used by the U.S. military and the various intelligence agencies for reconnaissance and communication.
According to Bloomberg, the report does not indicate whether the hackers behind the intrusions were state-sponsored or not, but it implies that the nature of the attacks and the targets seem to be consistent with Chinese military plans in case of open war, which include the disabling the enemy’s space systems and the ground infrastructure through which they are controlled.
According to the report, the control that the hackers had over the two satellites for those brief periods permitted them to damage or destroy them, or to block or falsify their transmission.
Since the satellites are controlled from the Svalbard Satellite Station in Norway which often uses the Internet to transfer and access files, it is deemed highly likely that the hackers have managed to insinuate themselves into the station's system through its Internet connection.