User-Agent Mozilla/5.0 (compatible; Yandex...) string identifies Yandex robots. Robots can send GET (for example, YandexBot/3.0) and HEAD (YandexWebmaster/2.0) requests to a server. A reverse DNS lookup can be used to check the authenticity of Yandex robots. More information can be found in the How to check that a robot belongs to Yandex section of the Webmaster help.
If you have any questions about our robots, please contact our support service: firstname.lastname@example.org. If you are experiencing technical issues with our robots we recommend attaching your server log.