A hacking group is sending out e-mails disguised as a South Korean governmental agency carrying out research on separated families of the two Koreas, a local security firm said Wednesday, claiming computer users should be extra cautious.

ESTsecurity Corp. said a hacker group, presumed to be "Geumseong121," is carrying out advanced persistent threat attacks by sending e-mails pretending to be official research.

The cyber security firm said the attack focused on attacking North Korea-related organizations in South Korea.

While the hacking group created image files including Korean-language texts by themselves, they also made a typo in English, ESTsecuirty said.

South and North Korea held Red Cross talks last month and agreed to hold family reunions from Aug. 20-26. The two Koreas technically remain at war as the 1950-53 Korean War ended only with an armistice, not a peace treaty.

The registered number of South Koreans wishing to meet their families or relatives in the North hovered above 130,000 as of the end of May, of which only about 57,000 remain alive. Most of them are in their 70s and older.

ESTsecurity said it has also found Russian codes in the attack, although it is presumed to be a "false flag" to deceive investigators. (Yonhap)