U.S. cybersecurity company Trend Micro said more than a dozen embassies in November were targeted by a virus attached to a blank email message.
"Whoever was responsible for this attack had the means, motivation and opportunity to carry out a targeted attack across multiple targets," the company said Monday. "This suggests a level of organization and available resources beyond ordinary cybercriminals."
Trend said body of the email was blank but contained a contaminated attachment which referred to the conflict in Syria.
"We do not know if the embassies were indeed affected by the malware mentioned or if there are other sets of targets, only that the samples received strongly suggest that the embassies were the intended recipients," the company said.
Trend said a similar attack was launched against Asian governments and members of Group of 20 major economic powers last year.
U.S. Army Maj. Gen. John Davis, a policy adviser for the military, said last year cybersecurity was fast becoming a top national security concern.