Hackers previously linked to North Korea by researchers at Google used an unknown vulnerability in Internet Explorer to target cybersecurity experts, according to a South Korean firm.

Two weeks ago, Google’s Threat Analysis Group (TAG) shocked the cybersecurity community by revealing a months-long social engineering campaign where hackers pretended to be fellow security researchers, tricking targets into collaborating on projects and viewing their blog. When researchers visited the website, a previously undiscovered zero-day vulnerability in Chrome infected some users with malware.

The same hackers, whom Google attributed to the North Korea-linked Lazarus Group, also