The report comes amid heightened fears of conflict on the Korean peninsula, fuelled by US President Donald Trump's continued threats of military action against Pyongyang to tame its weapons ambitions.
He said the Defense Department is confident in the security of its operations in Korea, including its ability to deal with threats from the North.
Senior diplomats of South Korea and the United States will hold a vice-ministerial strategic dialogue next week in Seoul, South Korea's foreign ministry said Wednesday.
While North Korea was not able to hack U.S. power companies, there are concerns among some of observers that the regime may attempt to damage the power grid by detonating a nuclear device at a high altitude above the U.S., triggering an electromagnetic pulse (EMP).
The hackers asked their victims to take part in a fundraiser in an email, according to a report by the internet security firm FireEye that was obtained by NBC News.
The trilateral meeting was last held in January in Washington. These attacks are also indicative of Pyongyang's efforts to showcase deterrent capabilities.
Trump will travel to South Korea as part of a visit to the region that will take place from Nov. 3-14 and will include stops in Japan, China, Vietnam, the Philippines and Hawaii.
The attacks linked to North Korea have been designed to interfere with the distribution of anti-North Korea propaganda and the acquisition of funds as the international community increases economic pressure on the regime, espionage, and possible retaliation. He also boasted that his nation has almost achieved a "balance of force" with the U.S.
"If the North Koreans in fact accessed the US/South Korean defense plans, this is a treasure trove of information and presents a real danger", said CNN military analyst and retired Lt. Col. Rick Francona.
Two bombers operating out of Andersen Air Force Base in Guam carried out the drills, US Pacific Air Forces said in a statement.
Tensions have soared between the United States and North Korea following a series of weapons tests by Pyongyang and a string of increasingly bellicose exchanges between Trump and North Korean leader Kim Jong Un. More ominously, Trump tweeted "only one thing will work" over the weekend.
DPRK is the acronym of North Korea's official name, the Democratic People's Republic of Korea. IBTimes UK has reached out to FireEye for further clarity on the campaign and is awaiting a response.
One defector from North Korea has said that the state's hacking capabilities are "beyond imagination".
The South Korean Unification Ministry could not confirm that the complex has been reopened, but did say that recent bus movements and illuminated street lamps in the site have been observed.