Here's how to fix this hack...
First, let me say that any web host could be susceptible to a skilled hacker. It's even happened to sites like YouTube, Twitter, Facebook, banks, government sites/hosting... you name it, all of which do everything possible to prevent these things from happening.
If you switch hosts, it could happen to your new host as well.
For GoDaddy users, here's how you fix this problem.
The good news is that this hack doesn't appear to do anything to your database, just all file extensions with the .php at the end.
First, back up your database and all your web hosting files (even though they are infected) to your computer. Always always always back things up.
Second, log into your web hosting control panel and go to your File Manager.
Click on the "History" button on the left (just above the list of your directory structure).
You should see then a list of all your files from previous days listed there. So if your site is hacked on May 1st, be sure you're looking at April 30th's backup. You should see the words "Changed" next to each file / folder which has been infected.
As a check, try opening the index.php file and make sure the base64 code is not located in there. If it's not, then you're probably good to go ahead and use this date's backup; if it's there, go back even further in your history.
Now that you know that date's files are clean, go back to your root folder (current date's folder) by clicking the "Current" button on the left.
Put a check mark next to all files and folders which which include .php files. This will include your wp-admin, wp-content, wp-includes folders as well as all your root files which end with .php.
Once those are all deleted, go back to your "History" button and to the date with clean files.
Check all the files which you had deleted from your Current area and then click "Restore" from the file menu above.
Once the restore is complete, you should be up and running.
Hope this helps. Also, you might want to check out how to help stop hacks from happening by visiting these sites:
Perishable Press 4G Blacklist