S. Korean president and defense ministry home pages were 'unavailable' 8 July 2009

South Korean Web sites were attacked again Thursday in a days-long assault that Seoul reportedly suspects North Korea is behind.

Some government Web sites have been affected in this third wave of Internet assaults, including the South Korean Defense Ministry and National Intelligence Service.  The Internet site of at least one Korean bank was also affected.

The South Korean news agency Yonhap cited government and industry officials as saying that the virus that has infected tens of thousands of computers appears to be programmed to automatically delete itself on Friday.

Lawmakers say the intelligence service told them Wednesday it suspects Pyongyang or its sympathizers could be involved in the attacks.  

Web sites in the United States that were targeted earlier this week appeared to have recovered Thursday.

In the United States, officials said Wednesday a days-long cyber attack had affected U.S. government Web sites including those of the White House, departments of Homeland Security, Defense, and Treasury, and the Voice of America.

In South Korea, earlier cyber attacks affected Web sites for the presidential office, ruling party, defense ministry and others.  

Computer experts describe this kind of 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.

If North Korea did carry out 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.