I was polygraphed back in 2015. They polygraphed me three times, and then said that I failed the question regarding unauthorized foreign contacts. It was a very bizarre experience. They would often repeat stuff like "Don't try to make anything happen or stop anything from happening. Got it!?" during the questioning. I remember having to sit perfectly still, with a pad under my bottom as well as under my feet.
Amusingly, before polygraphing me I was asked if I had "read anything online" about the process, to which I shrugged and said "Hasn't everybody?" The entire process is ridiculous.
Yandex is simply trying to introduce a barrier to deletion; several sites already use a CAPTCHA for this purpose (even if it's not used anywhere else). Should avoid using their service.