South Korea ? South Korea is learning more about the mysterious cyber attacks that targeted the country and its ally the United States, but the ultimate question of who the instigators are remained elusive.

The state-run Korea Communications Commission said Friday that it had identified and blocked five Internet Protocol, or IP, addresses in five countries used to distribute computer viruses that caused the wave of Web site outages in the two countries that began in the U.S. on July 4.

The IP addresses — the Web equivalent of a street address or phone number — may point to the computers that distributed the virus that triggered so-called denial of service attacks. In such assaults, floods of computers try to connect to a single site at the same time, overwhelming the server and making it inaccessible or unstable.

The addresses were in Austria, Georgia, Germany, South Korea and the U.S., a commission official said. He spoke on condition of anonymity because he is not authorized to speak to the media on the record.

Speculation over who was responsible for the attacks that targeted high-profile Web sites, including those of the White House and South Korea’s presidential Blue House, has centered on North Korea.