If you notice something strange about your Yandex account (for example, a friend got an email from you that you never sent or you see sites or programs you've never visited in your browsing history), then it's possible that your account was hacked.
To regain control of your account as quickly as possible, change your password and delete any unknown phone numbers or email addresses. Below you'll find step-by-step instructions.
Change your password and make sure that hackers can no longer access your account by doing the following:
Check that the Phone Numbers page only lists your numbers and that no secure numbers were changed or deleted.
Link your phone number to your account if you haven't already. A current phone number provides better account protection than an alternate email address or a security question.
Delete unfamiliar addresses on the My email addresses page.
Install an antivirus and firewall if you don't already have them in order to protect yourself from future viruses. Regularly scan your computer for viruses and don't forget to update your antivirus databases.
If you log in to Yandex using your social network account, make sure that your account was not hacked; hackers can get access to your Yandex data through Facebook, VK, etc.
If you use Android or iOS devices, then set up two-factor authentication, which is the most secure way to protect your Yandex account.
Read Protecting your account to find out reasons why your account might have been hacked and how to protect it.