PRAGUE -- Radio Free Europe/Radio Liberty has been targeted in an Internet attack known as a distributed denial of service (DDoS).
The attack has disrupted RFE/RL's global multimedia news and information services intermittently since November 14.
Nonetheless, its computer network was working on November 18 and broadcasts have continued normally.
The attack has not prevented the public from accessing RFE/RL's web pages.
But it has slowed the ability of RFE/RL's broadcasting services to upload fresh news stories, photographs, and video to the Internet.
RFE/RL President Kevin Klose said information is still being gathered about the attack, but he confirmed that it is believed to be "targeted."
Klose said a decision was taken on November 18 to report on the attack in response to the needs of the broadcasters' audiences, "who rely on RFE/RL reporting, and who themselves contend with countless obstacles to connect with us every day."
RFE/RL's content-management system also supports Voice of America, Middle East Broadcasting, and the Office of Cuba Broadcasting.
Those U.S. international media networks also have been adversely affected by the attacks but continue to operate.
Klose described the attack as "stark evidence of the challenges that confront the free dissemination and exchange of information in this age."
A DDoS attack floods the target with fake requests that come from thousands or even millions of computers that have been compromised or infected with viruses or malware.
RFE/RL experienced a more limited DDoS attack against its Belarusian language service in 2008.
RFE/RL Director of Technology Luke Springer said the latest attack was discovered on November 14 when hardware for the international media organization's computer network began receiving many times more requests than normal.
At the peak of the attack, the RFE/RL network was receiving requests for data from hundreds of thousands of computers every second.
Springer said that means there are probably more than 1 million malware-infected computers being directed by the attackers -- most likely without the knowledge of the computer owners.
Technical investigations show that nearly 80 percent of the computers sending out requests for data as part of the DDoS attack are in China and nearly 20 percent are in Russia.
But Springer said those findings do not indicate who is responsible for the attack.
Attempts to make technical changes that counter the attack have temporarily alleviated the problem. But Springer said the attackers also have been changing their methods, allowing them to continue disrupting services intermittently.
Springer said the DDoS attack has not damaged RFE/RL's network equipment. But he says that "filling up the Internet pipeline with so many bogus requests has caused a traffic jam."
RFE/RL is a private, nonprofit organization funded by a grant from the U.S. Congress.