Possible cause and solution:
First, hello everyone.
I made a website for a client and it stayed that way for 1 year until this week he contacted me saying that the website "had Malware".
I thought: Wow, cool the site was hacked... and I was right!
The page was being redirected to the url of the image attached to this comment.
In addition to the user with Administrator rights "wadminw"...
Right away I detected: Some Plugins were installed, several new files with random characters, and other system files were modified.
I tidied everything up... and did that general cleaning and updated what was needed.
Apparently everything is ok.
If you are not an advanced user and you don't have access to the files on the server, it will be difficult and you will probably need help....
This time I didn't need the BKP, but my tip is to always keep daily BKP's. Here I keep them for at least 7 days.
Good luck to everyone in this situation.