MOSCOW, Sept 9 (Reuters) - A cyber attack on Russian tech giant Yandex"s servers (YNDX.O) in August and September was the largest known distributed denial-of-service (DDoS) attack in the history of the internet, the company said on Thursday. The DDoS attack, in which hackers try to flood a network with unusually high volumes of data traffic in order to paralyse it when it can no longer cope with the scale of data requested, began in August and reached a record level on Sept. 5. "Our experts did manage to repel a record attack of nearly 22 million requests per second (RPS). This is the biggest known attack in the history of the internet," Yandex said in a statement. Yandex said it had seen 5.2 million RPS on Aug. 7, 6.5 million RPS on Aug. 9, 9.6 million RPS on Aug. 29, 10.9 million RPS on Aug. 31 and finally 21.8 million RPS on Sept. 5. U.S. cybersecurity firm Cloudflare (NET.N), which is widely used by businesses and other organisations to help defend against DDoS attacks, said in August the largest DDoS attack it was aware of reached 17.2 million RPS earlier this year. Cloudflare could not immediately be reached for comment on Thursday.