Hosting question

Hi Everyone,
I'm new here so sorry if this is in the wrong place.

I have a question about hosting and wanted to know if anyone has ever had this situation before.

I have a godaddy hosting account where i host about 10 domains being hosted on that account.

One of my buddies (no knowledge of websites) installed a malicious wordpress theme onto his sitethat is hosted by me and the site got hacked. I'm assuming it had some backdoor trojan in the theme that he installed. From there, it instantly spread to the other 10 websites and brought them all down.

Is there a way to seperate or create a barrier between the folders when they are on the same server?

I think you should update all your site's wordpress versions to the latest one and this will help.

Thats the part that I was worried about. When this happend, they were all the most current versions.

This problem has been fixed, but I'm wondering if I can going about my hosting the wrong way. Not sure how to have a hosting account that seperates all of the domains....

use a reseller account