The EU has announced an urgent investigation after suspected Chinese military hackers accessed thousands of sensitive diplomatic cables.
According to Agence France Presse, Area 1 Security, a US cybersecurity firm, said a unit of China's People's Liberation Army, acting on government orders, breached a secure communications network used by the EU to coordinate foreign policy.
The New York Times published some of the cables, which are from European Union diplomatic missions around the world and reveal anxiety about how to handle US President Donald Trump as well as concerns about the behavior of China, Russia and Iran.
Area 1, which was able to see the documents, said the attack targeted the EU, the United Nations and the AFL-CIO labor union in the US.
EU officials said they have begun a probe into the leak, which comes with Europe on high alert for malign online activity in the run-up to key parliamentary elections in May next year.
"The Council Secretariat is aware of allegations regarding a potential leak of sensitive information and is actively investigating the issue," the EU Council, which represents member states, said.
"The Council Secretariat does not comment on allegations nor on matters relating to operational security. The Council Secretariat takes the security of its facilities, including its IT systems, extremely seriously."
Area 1 said the hackers gained access to the diplomatic communications network after a simple "phishing" campaign targeting the foreign ministry in Cyprus with mails designed to trick them into downloading hacking tools.
Diplomatic sources said Cyprus has begun its own investigation and asked other EU countries for technical help.
Once inside the EU system, the hackers extracted thousands of diplomatic cables, most of which have a low security classification according to the New York Times, which was given 1,100 by Area 1 and published a selection.
Many of the cables are run-of-the-mill weekly reports from missions around the world, detailing conversations with leaders and officials, the NYT said.
But there is also analysis of trends in global politics and trade, particularly on China's changing role under President Xi Jinping and relations with Russia and the US, and tantalizing glimpses into closed-door meetings.
In one cable, the EU's diplomatic mission in Moscow describes the controversial summit in Helsinki in July between Trump and Russian President Vladimir Putin as "successful (at least for Putin)".
Another gives a detailed account of a meeting with President Xi in which he rails against Trump's trade tactics, saying the US was "behaving as if it was fighting in a no-rules freestyle boxing match" and vowing not to give in to "bullying".
In a somewhat ironic turn, the account describes Chinese Premier Li Keqiang assuring EU President Donald Tusk of Beijing's "steadfast opposition to cyber-attacks and hacking".
There are extensive reports on the situation in Ukraine, where a conflict rumbles on between government forces and pro-Russian separatists.
These include a warning from a senior Ukrainian official, dating from February, that Moscow may already have deployed nuclear warheads in Crimea, which it annexed in 2014.
