This week's cyber attacks on South Korea are believed to have been mounted from 16 different countries, Seoul's spy agency was quoted as saying on Friday.
The National Intelligence Service (NIS) reportedly told legislators the attacks were tracked to 86 Internet protocol addresses from 16 countries including the United States, Japan and China.
The lawmakers, quoting information from the NIS given in a closed briefing, said North Korea was not among the 16 countries.
On Wednesday the spy agency told parliament's intelligence committee that it believes the communist North or its sympathisers may be to blame for the attacks.
A third wave of cyber attacks hit South Korea on Thursday evening, blocking or impeding access to official and private websites.
The US State Department said its website also came under attack for a fourth day. The White House and Pentagon websites were among US government entities targeted earlier this week.
Hackers have planted viruses in thousands of personal computers in South Korea and overseas.
In what is called a "distributed denial of service," they are programmed to swamp certain US and South Korean websites at selected times.