Hackers have targeted government officials of more than 20 countries, including Ireland and Romania, in a sophisticated online attack.
The breach was detected by Kaspersky Lab, which dubbed the attack "MiniDuke".
The company found that victims' computers were infected via a modified Adobe PDF email attachment, and the perpetrators were operating from servers based in Panama and Turkey. Last week Adobe released an update that patches the Adobe PDF bug used in the attack.
According to Vitaly Kamluk, Kaspersky Lab's Chief Malware Expert, the precise information being targeted was unclear. "It's currently unclear what the attackers were after. But the interest in these high-profile victims is quite obvious," he said.
MiniDuke has infiltrated computers belonging to governments including Ireland, Romania, Portugal, Belgium and the Czech Republic, as well as a Hungarian research foundation and a US healthcare provider.
Eugene Kaspersky, founder of Kaspersky Lab, described it as a very unusual attack, saying: "I remember this style of malicious programming from the end of the 1990s and the beginning of the 2000s. I wonder if these types of malware writers, who have been in hibernation for more than a decade, have suddenly awoken and joined the sophisticated group of threat actors active in the cyber world."