Chinese hackers spied on the computers of five European foreign ministries over the summer, according to research from US security company FireEye.
The hackers sent emails with malware-ridden attachments purporting to detail a possible US intervention in Syria.
The company has not revealed which ministries were targeted but said the malware samples were meant for individuals involved in the G20 talks.
The researchers say they were able to observe the hackers for about a week.
In total nine computers had been compromised, the company told the BBC.