Site was Hacked/Need help repairing damage

http://shinobifablesuntold.forumotion.com/

^My forum.

It was hacked by someone with the account name "Hideki". This is the third time the same person has attacked our site by posting some strange code in reply to our system/rule pages. When he does this the page becomes blank and there is blasting music in place of any imagery or information.

He has done this on thirty four pages or so, and they are within the following forums:

http://shinobifablesuntold.forumotion.com/f1-systems-and-guidelines
http://shinobifablesuntold.forumotion.com/f24-clan-information
http://shinobifablesuntold.forumotion.com/f12-canon-information
http://shinobifablesuntold.forumotion.com/f18-news-and-events

^Could I please get someone to come on my forum and help disable these codes, as well as show me procedure to remove them in the future if this should happen again?

Hehe, this guy makes me remember that i used to do the same thing as him XD so funny.
This isnt hack, just a trick XD
He used this code:

Code:

<audio controls autoplay><source src="https://track3.mixtape.moe/gjxsxp.webm" type="audio/ogg"><br /> <source src="https://track3.mixtape.moe/gjxsxp.webm" type="audio/mpeg"></audio><style>div{display:none; visibility:hidden;}</style>‏

If you want to fix:
1. Go ACP > General > Messages and e-mails > Configuration > Allow HTML: No
Or if you wan to keep the html, you can use Word censoring (make him cant use style tag):
2. Go ACP > General > Messages and e-mails > Censoring > Word Censoring > Add new word:

Code:

World: <style> Replacement: <oppagangnamstyle>

BAM!