DONALD Trump inherited a secret cyber war with North Korea and was warned its missile program would remain his biggest international challenge.

Mr Obama also undertook a series of cyberattacks against North Korea’s missile program as he believed anti-missile systems were inadequate to protect the US from a potential threat.

The revelations from a New York Timesinvestigation come as Pyongyang today fired four ballistic missiles, three of which landed in Japan’s Exclusive Economic Zone.

The brazen move sent alarm bells ringing along the Korean peninsula, with Seoul and Tokyo both expressing concerns.

The launch also comes as the Times revealed that Mr Trump’s advisers are now considering whether to continue with the cyber attacks, which the Obama administration began in 2014.

The attacks began because Mr Obama concluded traditional anti-missile systems weren’t enough to protect his country.

President Obama reportedly chose to target missiles before test launches took place, ultimately sabotaging them within seconds.

Details of the program were not released at the request of national security officials, however several missile launches failed or veered off course after the US implemented the Obama strategy.

It remains unclear whether this could also be due to other factors such as manufacturing or human error.

Dr Greg Austin, a Professor in the Australian Centre for Cyber Security at the University of New South Wales in Canberra, said the Obama administration had publicly stated it would retaliate against a North Korean missile launch for its past cyber attacks on US targets, especially against Sony pictures.

Dr Austin said the news of inclusion of cyber attacks against North Korean missiles in that suite of options is bit of a surprise.

However while he said while the Times article was credible, it left some room to question around the edges.

“The US Government does not believe, in my view, that it had the capabilities to take down every North Korean missile in a cyber attack,” Dr Austin said.

He said he didn’t believe the cyber attacks occurred purely because of a weakness in ground-based anti-ballistic missile system as the article suggested.

Asked how a Trump administration should deal with the North Korea problem, Dr Austin said it didn’t fit neatly in the President’s simplistic world view.

Dr Austin said any action would ultimately be guided by Mr Trump’s intelligence and military advisers who would probably take similar action as Mr Obama did.

“It is true he has inherited the North Korea problem,” he said.

“Donald Trump has indicated he will act militarily against North Korea if it threatened the US, but it’s clear it’s not in anyone’s interests to resort to combat action unless North Korea actually commits an act of war.”

Dr Austin also said the reality was the President was more concerned with bigger issues such as Islamic State and North Korea wasn’t on his radar ideologically or politically.

He said Mr Trump hasn’t given clear guidance on what exactly his policy is on North Korea and the New York Times headline was simply reminding him what he has inherited.

DEFIANT PYONGYANG

North Korean leader Kim Jong-un has repeatedly claimed his country is in “the final stage in preparations” for the inaugural test of his intercontinental missiles, raising global concerns North Korea today fired four banned ballistic missiles that flew about 1000 kilometres into Japan’s exclusive economic zone in an apparent reaction to huge military drills by Washington and Seoul that Pyongyang insists are an invasion rehearsal.

It was not immediately clear the exact type of missile fired, however Pyongyang has staged a series of missile test-launches of various ranges in recent months, including a new intermediate-range missile in February.

Kim Jong-un has also been pushing for a nuclear and missile program that can deter what he calls US and South Korean hostility toward the North.

Japanese Prime Minister Shinzo Abe said today’s missile launch showed that North Korea has become “a new kind of threat”.

North Korea's internet 'shut down' North Korea's internet 'shut down'

South Korea’s joint Chief of Staff said in a statement that today’s launches were made from the Tongchang-ri area in North Pyongyang province, which is home to North’s Seohae Satellite Station where it has conducted prohibited long-range rocket launches in recent years.

Seoul and Washington call their military drills on the Korean Peninsula, which remains in a technical state of war because the 1950-53 Korean War ended with an armistice and not a peace treaty, defensive and routine.

The launch comes amid widespread concern that the North will conduct an ICBM test that, when perfected, could in theory reach US shores. Washington would consider such a capability a major threat.

The United States has 28,500 troops stationed in South Korea, and 50,000 in Japan, as a deterrent against a potential aggression from the North.

debra.killalea@news.com.au