RSS feed error

Hello!
My RSS feed seems to get error on all WP powered blogs.

This page contains the following errors:

error on line 218 at column 1: Extra content at the end of the document
Below is a rendering of the page up to the first error.

I tried to upgrade wordpress but it didn’t fix.

Theres also files named upd.php and 44012e792781772d8795acf27fabed2f.php

Does anyone know how I can fix my feed?
and help me figure out what these files are.
I’m afraid if I got hacked…