First make sure you have antivirus protection on your devices. Then log into Yandex.Passport and complete the following:
- In the Email and phone numbers section, delete all phone numbers and email addresses that aren't yours and link your current number to your account.
- In the Log in history and devices section, disable all devices that aren't yours, delete unknown programs and tap the Not me button to mark all actions that aren't yours.
- In the Passwords and login section, change your password and set up two-factor authentication.
Check out the Yandex.Passport Help section for more on security and strong passwords.