Why is it redirected to a non-existent page?

Question

linux

Good day! There is a website running on wordpress 4.3. Today we have a strange problem.
You go to the site page - it loads, but at the end of the download it is automatically redirected to a non-existent page of the form

login/

, where login is my real admin login, but in small case.
Tried to update to Wp 4.4, delete htaccess, remove all plugins - nothing helps.
Tell me where to dig?
Thanks in advance!

Answer 1

My feeling is that you have been hacked. Maybe I'm wrong.
It's a pity you worked without VCS. Everything would be easier.
In any case, if I were you,
I would download all today's code to a LAN, and start searching through the sources.
With the help of IDE (in them, as a rule, searching through project files is faster due to indexing)
Mostly, I would search in the template folder first.
You can start the search with approximately the following functions:
is_user_logged_in
is_admin
current_user_can
is_super_admin
Then where the thought will lead.
After a thousand unsuccessful attempts, you can go through some Manul'om on the source.
https://yandex.ru/promo/manul#about