Some Hands-on analysis is required...
in terminal on the infected host...
Do NOT run this as root unless it's run from the users' /home/$user directory
find `pwd` -name *.php -exec grep base64_decode {} \; > ~/infected.out
then let's count the number of infected files...
nl ~/infected.out | tail -1
Then check the ~/infected.out file manually and see what's what.
I'd need the first 15 characters or so of everything after "decode(""
and will resemble this (base64_decode("DQpzZXRfdGltZV9saW1p
How this stuff got there, I can only imagine (777 DIRs) or a stolen account password, but that's another day.
If you don't find and/or plug the hole, this will most likely repeat itself.
"It is interesting that the infection has spread to all subdomains and parked domains"
Not really. The first thing any decent hacker script does is look for more exploitable weaknesses in Security, and they LOVE those 777 directories.
"Is there a solution for this malware on the site?"
Yes, is WordPress up-to-date/latest?
Is this shared hosting, VPS, or a Dedicated Server?
I'd bet $20.00 this is a cPanel host.
The 5433712.php type files are usually reverse-shells.
You can PM me for a more in-depth course of cleaning or further diagnostics.
The cleaner script is a one-liner.
HTH.