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

U.S. and South Korean government Web sites have been disrupted in what officials are calling a widespread and coordinated cyber attack.

U.S. officials said the attack targeted U.S. government Web sites including that of the White House, departments of Homeland Security, Defense, and Treasury, and The Voice of America.

The officials said the attacks began July 4.  

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

South Korea's National Intelligence Service reportedly said it suspects North Korea could be involved, saying such a coordinated attack is likely the work of a large organization or state.

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.

VOA Internet Office Director Michael Messinger said visits to the agency's Web site are down by about 40,000 a day.  He said although difficult to pinpoint, the attack appears to have originated in South Korea.  He said the attack has caused a "significant disruption" to the VOA servers.

U.S. officials were quoted as saying the New York Stock Exchange and other financial institution Web sites also came under attack.

South Korean authorities issued a security warning Wednesday after several major government agencies and financial institutions were disabled by apparent hacker attacks.

Some information for this report was provided by AFP, AP and Reuters.