How to check that a robot belongs to Yandex
Some robots can disguise themselves by specifying the user-agent. You can check the authenticity of a robot using reverse DNS lookups.
Please follow these instructions:
Determine the IP address of the user-agent in question using your server logs. All Yandex robots are represented by a specified user-agent.
Use a DNS lookup of the IP address to determine the host domain.
You may use the domain name to check whether or not a robot belongs to Yandex. All Yandex robots have names ending in “yandex.ru”, “yandex.net” or “yandex.com”. If the host's name has a different ending the robot does not belong to Yandex.
Finally, make sure that the name is correct. To do this use a forward DNS lookup, to determine the IP address corresponding to the host name. They should match the IP address used in the DNS lookup. If the IP addresses do not match it means that the host name is false.