I have 7 websites on a Plesk server. All have many 'WordPress Instances' active.
Have re-loaded several past back-up copies; all pre-dated this disaster; to no good effect!!
Created a new 'WordPress Instance' (i.e. no virus) and immedately had the same problem.
Have used 'WP Lock Pages plugin', which has prevented this return to default from happening immediately, but only defers for and hour or anything up to a day!!!
But this does briefly allow URL wp logins (with the default My CMS Site Name,the browser login option does not respond).
Any ideas/solutions desperately needed, please?
I am a WYSIWYG user, so not good with too much coding, but always willing to learn.
Thanks in advance,