The North Korean government hacked South Korean's phones by creating a mobile game that contained malicious software, according to South Korea’s National Intelligence Service. NIS officials didn’t report any damage or theft but estimated that more than 20,000 smartphone owners have given Pyongyang a window into their lives.

NIS agents said the nefarious app was available on South Korean websites between May 19 and Sept. 16, according to a government document obtained by South Korea’s Yonhap news agency. The intelligence agency didn’t mention any specific apps, saying only that the websites have been taken down and that South Korean cybersecurity has been updated.

The timing of the government report coincides with a South Korean technology expert’s announcement that a popular game called “Nice Pigs” was designed and released by a member of North Korea’s Korea Computer Center. Kang Jin-gyu, the proprietor of Digital Hurricane, a technology research site, told the Pyonyang-centric that, in the process of researching the game’s origin, he discovered that the game’s creator was one of thousands of North Koreans who aid the Communist country from outside its borders.

“The website was registered with an Indian IP address, but I tracked down the IP of the address of the one who opened the website and it turns out this person moved from North Korea to India,” he told the news service. “The website kept changing its appearance, as if it didn’t want to look like it was run by North Korean people.”

The Nice Pigs web page has since been blocked. 

Various intelligence and cybersecurity reports published in recent years have suggested that North Korean hackers trained by Russian, Chinese and Indian agencies have turned their focus on South Korean banks and other institutions. Researchers at the Kaspersky cybersecurity firm told the UK's Guardian newspaper that in the past hackers have deployed spyware specifically designed to steal and monitor Hangul word processor (HWP) documents, which are favored by South Korean leaders.

“We don’t know exactly what was stolen but we suspect they were looking for all sorts of HWP documents relating to work done by think tanks towards unification and on defense and security strategy,” Kaspersky research director Costin Raiu told the British outlet last year.