This does not look familiar.
Let site support know about it.

Larmu, I'll had user evading my sites, but never got a message like this one. Usually word press will send an email when a new user joint you site. Follow through with other's advice.

I hope you get to the bottom of this situation.

Much Luck!
Louisa B

Yeah I would report that in to be on safe side since you're not aware of it

I am suspicious of @mail.RU I have found most are link-backs and spammers. Check it out carefully,

Get advice from other WA members as I am not the most experienced WAer.

That message appears as though you have added a new User to your site.

You should go to the Dashboard of your website and click on 'Users'. That is where you will see your own details, and details of anyone else you have given permission to become a User of your website.

If you haven't given permission to this person, then you need to delete them.

Sounds like you have a visitor doing something for you on your site.