The USA’s cyber-defences are coming under increasing strain, with fresh reports detailing efforts from foreign adversaries to expose the country’s critical operations; including the military and energy industry.

The latest blow to the military comes after hackers leaked personal details belonging to tens of thousands of US troops online. The attack was identified by security researchers in South Korea, which saw government and media websites shut down from cyber-attacks yesterday in an apparent link to the anniversary of the Korean War with its Northern neighbours.

The unidentified hackers claim to have secured and released details of over two million South Korean ruling party workers as well as 40,000 US military staff, reports Reuters. The claims have been supported by South Korean security firm NSHC, which said, "We have seen the sites where the details were posted and clips that supposedly capture the process of hacking into web sites."

The US military in South Korea did not immediately comment on the incident.

News of the attack arrives as the Council on Foreign Relations (CFR), an American non-profit group, warns that the country’s oil and natural gas operations are also coming under siege from hackers.

Citing data from security company Alert Logic, the FCR said America’s energy companies were targeted by more malware attacks than any other industry from April to September last year. Cyber-espionage campaigns were sounded out as a particularly critical problem, with foreign governments attempting to access long-term strategic plans for the sector, bids made for new drilling land, and communications with international officials, Reuters reports.

The findings will deepen concerns over cyber-espionage attacks within the US. Internet security firm Mandiant claimed a military base in Shanghai was spying on much of the country’s key operations, while government officials have accused Chinese companies of stealing intellectual property via cyber-attacks.

With the States coming under so much pressure in the digital realm, security expert Philip Lieberman said the country was on the brink of suffering a major cyber-assault that would cripple the US’s national infrastructure.

President Obama has been mindful of the growing threats, this year passing an executive order aimed at bolstering America’s offensive and defensive cyber capabilities.