Hi esmi,
For the last 4 days, the server only had WP installed, even with a “Quota” setting, meaning no scripts running on the domain could have accessed any files outside the domain/respective file system (new owner ID).
And vice versa, no outside script should’ve (if that possible with no extra server content) been able to add those files in a file system belonging to another owner.
Hence, it’s got to be coming in through WP.
Also, the log files show frequent (<5min around the clock!) attempts to run those Malware files such as auth.php, commonn.php, and more recently real, legit files they compromised.
F.