WASHINGTON, (Reuters) – More than two dozen Internet  sites in South Korea and the United States, including the White  House, were attacked in recent days by hackers that South  Korea’s spy agency said may be linked to North Korea.

The attacks began on July 4, the U.S. Independence Day  holiday, and were widespread, but government websites were now  up and running and day-to-day operations at the White House and  Pentagon had not been affected, officials said.

U.S. officials also said it was premature to say who was  responsible and that these types of Internet attacks happen  everyday on government networks.

South Korea’s National Intelligence Service said in a  statement that an organization and possibly a state were behind  the attacks in South Korea, the world’s most wired nation, and  there were signs of “meticulous preparations” for the act.

South Korean media, including Yonhap news agency, quoted  parliament members as saying after an intelligence briefing  that the spy agency believed “North Korea or pro-North  elements” were behind the attacks that targeted 26 U.S. and  South Korean websites.

In the United States, the NASDAQ stock market said its  website and business were unaffected by the attack and the  White House said all federal websites were “up and running.”

The attack on websites had “absolutely no effect” on  day-to-day operations at the White House, spokesman Nick  Shapiro said.