A North Korean hacker group was found to have attempted to hack some 900 South Korean experts on foreign affairs and security by impersonating legitimate organizations via email.

According to the National Police Agency on Sunday, the group sent “phishing emails” in April under the names of reporters covering the presidential transition committee as well as the name of a secretary of North Korean-born South Korean lawmaker Tae Yong-ho in May.

The group posed as the Korea National Diplomatic Academy when sending such emails to experts in October, with at least 892 targets receiving the scam emails.

Police estimate that 49 recipients logged in to the phishing websites, most of whom were researchers at private organizations or college professors, but no intelligence on foreign affairs or security was leaked.

In the successful hacking attempts, the North Korean group distributed ransomware, a form of malicious software or malware that locks up a victim’s data or computer networks and is unlocked by the perpetrator in exchange for a ransom.

The hacking group demanded bitcoins as a condition to get rid of the malware, the first time a North Korean hacking operation has included a demand for money.

Police believe the North Korean hacking group known as "Kimsuky,” which led the 2014 hacking of the Korea Hydro and Nuclear Power Company, was behind the latest attempts.