Many Yandex services are available only after you register: for example, you need an account to use Yandex Mail, Yandex Disk, and Yandex Webmaster.
If you used someone else's phone and forgot to log out from your Yandex ID or you suspect that your Yandex ID has been hacked, you can log out on all devices:
- Go to Account management.
- In the Logins and devices section, press Log out on all devices.
- Log in to your Yandex ID again on all devices and in all apps that you use.