Drupal Sending tons of Spam email

Question

Apparently one of the modules installed on my drupal site has been sending SPAM emails from my server as in (name)_(lastname)@(myservername).com , it managed to send 1000 email and queue 97,000 emails only in the first day..

At first, based on the email details, I figured it was being sent from a PHP page called diff.php under /sites/all/modules/contrib/libraries/tests/libraries/diff.php, so I deleted the whole tests folder, but now the emails are heading directly from my root site.. I have installed Hacked! to a development copy, and here's a copy of the results:

Does it seem like a module issue? should I re-install the changed modules?