What is this code

Hello.

I just received an email from my hosting company saying I have suspicious files in my hosting account. I host 2 WP sites in it.
I checked at last date modified files and folders and indeed there are modifications over the night although I didn’t signed in in over 2 months.
404.model.php
model.php
post.php.suspected

Those are the files and this is the code in one file post.php

MALWARE DELETED

what code is that? I opened it in my browser it can affect my pc?
how do I get rid of that? why and how did it got there?