unknown users

Hi!
I have a problem ... from time to time in the backend of the site there are " new unknown users ." Moreover , the button " Log in " non-existent on my site. where they come from ? And how to make sure that they do not appear again?

Hi,
if they have e-mails from yahoo or from Russian domain they are spammers.

But in general, if you don't want to have new registrations you have to disable it in User Options.
Because Joomla have built-in static url for registration and login which you cannot disable.

You can also:
1) add ReCaptcha for registration (install plugin). Not old Capchta!!!
2) If you have J2.5, install http://www.abivia.net/products/joomla-e ... ser-killer

Thank you for such a quick response !!!
Happy New Year !