PHP Malware Scanner and false positives

My site is being continually infected and I’m trying to find the cause. I’ve been using PHP Malware Scanner which works great but it keeps saying that the following files are infected but I can’t seem to see anything out of the ordinary:

/public_html/core/components/upgrademodx/vendor/guzzlehttp/guzzle/src/Middleware.php
/public_html/core/packages/upgrademodx-2.1.2-pl/modCategory/178a0f9304ec11c49bc2c26b2e8a500f/0/upgrademodx/vendor/guzzlehttp/guzzle/src/Middleware.php
/public_html/core/model/phpthumb/phpthumb.class.php

Are these false positives?