The National Police Agency said Thursday it suspects eight computer servers in Japan were involved in a wave of attacks in July on government and commercial Web sites in South Korea and the U.S. and a North Korean connection is suspected.

Police found a program on the servers for issuing instructions to terminals outside of Japan to send large amounts of data.

The denial-of-service attack in July overloaded the Web servers of 35 government and private organizations in the two countries, including the South Korean presidential office.

However, it is not clear whether the Japanese servers originated the instructions to the terminals that sent the large amounts of data, the NPA said.

Tokyo and Seoul are trying to identify the servers.