Harmful code has been detected

A piece of harmful code has been detected on my website. The specific location of the code is /plugin/ad-inserter-pro/class.php, specifically on line 644.

The code in question is as follows: eval ("?>" . $code . "<?php ");

I kindly request immediate assistance in resolving this matter, as the mentioned code is prone to execution within the context of the calling “eval()” function. Consequently, any variables that are established or modified within this “eval()” call might persist even after its execution has concluded. Your prompt attention to this issue would be greatly appreciated.