WASHINGTON – The powerful attack that overwhelmed computers at U.S. and South Korean government agencies for days was even broader than initially realized, also targeting the White House, the Pentagon and the New York Stock Exchange.
Other targets of the attack included the National Security Agency, Homeland Security Department, State Department, the Nasdaq stock market and The Washington Post, according to an early analysis of the malicious software used in the attacks.
Many of the organizations appeared to successfully blunt the sustained computer assaults.
The Associated Press obtained the target list from security experts analyzing the attacks. It was not immediately clear who might be responsible or what their motives were.
South Korean intelligence officials believe the attacks were carried out by North Korea or pro-Pyongyang forces.
The attack was remarkably successful in limiting public access to victim Web sites, but internal e-mail systems are typically unaffected in such attacks.
Some government Web sites — such as the Treasury Department, Federal Trade Commission and Secret Service — were still reporting problems days after the attack started during the July 4 holiday.
The South Korean sites included the presidential Blue House, the Defense Ministry, the National Assembly, Shinhan Bank, Korea Exchange Bank and top Internet portal Naver.
They went down or had access problems since late Tuesday, said Ahn Jeong-eun, a spokeswoman at the Korea Information Security Agency.
South Korea's National Intelligence Service, the nation's principal spy agency, told a group of South Korean lawmakers Wednesday it believes that North Korea or North Korean sympathizers in the South were behind the attacks, according to an aide to one of the lawmakers briefed on the information.
The aide spoke on condition of anonymity, citing the sensitivity of the information. The National Intelligence Service said it couldn't immediately confirm the report, but it said it was cooperating with American authorities.
The attacks will be difficult to trace, said Professor Peter Sommer, an expert on cyberterrorism at the London School of Economics.
"Even if you are right about the fact of being attacked, initial diagnoses are often wrong," he said Wednesday.
Amy Kudwa, spokeswoman for the Homeland Security Department, said the agency's U.S. Computer Emergency Readiness Team issued a notice to federal departments and other partner organizations about the problems and "advised them of steps to take to help mitigate against such attacks."
The U.S., she said, sees attacks on its networks every day, and measures have been put in place to minimize the impact on federal Web sites.
Kudwa had no comment on the South Korean attacks.
New York Stock Exchange spokesman Ray Pellecchia could not confirm the attack, saying the company does not comment on security issues.
Others familiar with the U.S. outage, which is called a denial of service attack, said the fact that the government Web sites were still being affected three days after it began signaled an unusually lengthy and sophisticated attack.
Attacks on federal computer networks are common, ranging from nuisance hacking to more serious assaults, sometimes blamed on China. U.S. security officials also worry about cyber attacks from Al Qaeda or other terrorists.
This time, two government officials acknowledged that the Treasury and Secret Service sites were brought down, and said the agencies were working with their Internet service provider to resolve the problem.
The officials spoke on condition of anonymity because they were not authorized to speak on the matter.
Ben Rushlo, director of Internet technologies at Keynote Systems, said problems with the Transportation Department site began Saturday and continued until Monday, while the FTC site was down Sunday and Monday.
Keynote Systems is a mobile and Web site monitoring company based in San Mateo, Calif. The company publishes data detailing outages on Web sites, including 40 government sites it watches.
According to Rushlo, the Transportation Web site was "100 percent down" for two days, so that no Internet users could get through to it.
"This is very strange. You don't see this," he said. "Having something 100 percent down for a 24-hour-plus period is a pretty significant event."
He added that, "The fact that it lasted for so long and that it was so significant in its ability to bring the site down says something about the site's ability to fend off (an attack) or about the severity of the attack."
The FTC site, meanwhile, started to come back online late Sunday, but even on Tuesday Internet users still were unable to get to the site 70 percent of the time.
Web sites of major South Korean government agencies, including the presidential Blue House and the Defense Ministry, and some banking sites were paralyzed Tuesday.
An initial investigation found that many personal computers were infected with a virus ordering them to visit major official Web sites in South Korea and the U.S. at the same time, Korea Information Security Agency official Shin Hwa-su said.
Denial of service attacks against Web sites are not uncommon, and are usually caused when sites are deluged with Internet traffic so as to effectively take them off-line.
Mounting such an attack can be relatively easy using widely available hacking programs, and they can be made far more serious if hackers infect and use thousands of computers tied together into "botnets."
For instance, last summer, in the weeks leading up to the war between Russia and Georgia, Georgian government and corporate Web sites began to see "denial of service" attacks.
The Kremlin denied involvement, but a group of independent Western computer experts traced domain names and Web site registration data to conclude that the Russian security and military intelligence agencies were involved.
Documenting cyber attacks against government sites is difficult, and depends heavily on how agencies characterize an incident and how successful or damaging it is.
Government officials routinely say their computers are probed millions of times a day, with many of those being scans that don't trigger any problems.
In a June report, the congressional Government Accountability Office said federal agencies reported more than 16,000 threats or incidents last year, roughly three times the amount in 2007.
Most of those involved unauthorized access to the system, violations of computer use policies or investigations into potentially harmful incidents.
The Homeland Security Department, meanwhile, says there were 5,499 known breaches of U.S. government computers in 2008, up from 3,928 the previous year, and just 2,172 in 2006.