The spy agencies of South Korea and Germany have issued a joint security advisory warning of the risks of cyber attacks by "Kimsuky," a North Korean hacking group.

South Korea's National Intelligence Service(NIS) and its German counterpart Federal Constitutional Protection Agency (BfV) issued the advisory, saying that Kimsuky's hacking methods are becoming more sophisticated recently, exploiting Google services in its recent attacks.

According to the advisory, one of the hacking methods is to steal the contents of the victim's emails in real time by leading them to install a malicious Chromium-based browser extension at Google Chrome. 

Another major hacking technique is using the Google Play sync function and leading the victim to install malicious apps on smartphones.

The NIS said that most of Kimsuky's recent attacks linked to North Korea's Reconnaissance General Bureau are being carried out through spear phishing, urging users to learn how to identify malicious e-mails themselves and to follow precautions when receiving suspicious e-mails.