The DDoS attack began in August and reached a record level on 5 September when the outfit's security team managed 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.
The previous record was held by Cloudflare, which said last month that it had mitigated a 17.2 RPS DDoS attack. DDoS attacks used to be the weapon of choice of hackers for many years, but have not been hitting the headlines so much because of the success of ransomware attacks.