North Korea attempted to hack into South Koreans' smartphones by spreading malicious applications online, possibly infecting more than 20,000 smartphones, Seoul's spy agency said Wednesday.

The malicious applications, disguised as games, were spread on South Korean websites between May 19 and Sept. 16, according to a report submitted to the parliamentary intelligence committee by the National Intelligence Service (NIS).

Although the NIS did not report any actual damage, it estimated that more than 20,000 smartphones in South Korea may have been infected by the applications.

The NIS said it worked with the websites' owners and the government to remove the applications, block relevant hacking channels and update computer vaccines.

North Korea is known to operate a wide network of elite hackers from within and outside its borders to conduct cyber attacks on the websites of South Korean government offices, banks and media outlets.

In July, military sources said that the communist state appears to have doubled its number of elite hackers over the past two years to 5,900 personnel. (Yonhap)