S. Korean president and defense ministry home pages were "unavailable" on July 8, 2009

Some South Korean officials say there may be more evidence North Korea launched a series of cyber attacks that hit Web sites around the world.

According to South Korean news reports from the Yonhap news agency and the JoongAng Ilbo newspaper Saturday, the country's spy agency obtained documents ordering a North Korean army unit to start the attack.

The reports say some top South Korean lawmakers were briefed on the evidence earlier this week.  But the National Intelligence Service says it cannot confirm the reports.

The multi-day cyber attack affected government Web sites in South Korea and the United States.  The Korea Communications Commission warned Friday a new phase of the virus could destroy the data of thousands of personal computers in South Korea.

If North Korea did play a role in the cyber attacks, it would represent a further escalation of tensions on the Korean peninsula between Pyongyang and Seoul.  

North Korea has engaged in a series of long and short-range missile tests in recent months, as well as a nuclear test back in May.

Computer experts describe this week's attack as a "distributed denial of service."  A computer virus spreads from one personal computer to another, directing data traffic from those computers to the targeted Web sites.

The attacks hit the South Korean Defense Ministry, Intelligence Service and at least one Korean bank.  In the United States, Web sites for the White House, departments of Homeland Security, Defense, and Treasury, and the Voice of America were also targeted.

South Korean intelligence officials say the attackers used 86 Internet Protocol addresses in 16 nations, including South Korea, Japan, China and the United States, to launch the cyber strikes.

Some information for this report was provided by AP.