PCs could be hit next in Web attack - South Korea

* New attacks likely at 1500 GMT

* Personal computer hard disks could be damaged

* North Korea may not be to blame - experts

By Jon Herskovitz

SEOUL, July 10 (Reuters) - Cyber attacks slowing U.S. and South Korean websites could enter a new phase on Friday by attacking personal computers and wiping hard disks, a South Korean government agency and Web security firm said.

North Korea was originally a prime suspect for launching the cyber attacks, but the isolated state was not named on a list of five countries where the attacks may have originated, the Korea Communications Commission (KCC) said.

The attacks targeting dozens of government and business sites in South Korea and the United States did not caused major damage or security breaches, experts said, but the KCC warned a new phase at 1500 GMT on Friday that could cause severe damage.

Leading South Korean Web security firm Ahnlab said data stored on tens of thousands of affected computers could be damaged.

"The affected computers will not be able to boot and their storage files will be disabled," said Lee Byung-cheol of Ahnlab.

FIVE COUNTRIES NAMED

The commission said host Web sites believed behind the original attacks were based in Germany, Austria, the United States, Georgia and South Korea.

South Koreans lawmakers briefed by the National Intelligence Service said although North Korea was not one of the list, Pyongyang was still seen as a likely suspects.

Internet access is denied to almost everyone in impoverished North Korea, but intelligence sources say leader Kim Jong-il launched a cyber warfare unit several years ago.

Some analysts questioned the North's involvement, saying it may be the work of industrial spies or pranksters.[ID:nN08404460]

The attacks saturated target websites with access requests generated by malicious software planted on personal computers. This overwhelmed some targeted sites and slowed server response to legitimate traffic.

The so-called "distributed denial of service" hacking attack spreads viruses on PCs, turning them into zombies to simultaneously connect to specific sites, unbeknownst to owners, experts said.

U.S. officials would not speculate on who might be behind the attacks but noted that U.S. government websites face attacks or scams "millions of times" a day. (Additional reporting by Rhee So-eui and Christine Kim; Editing by David Fox)