Hacked Board/SQL Injection
 

I just did a search for a page on my site in google and have found loads of indexed spam pages that I was unware of. When I click on them I get a bad gateway message, but google has the cache for some of the pages:

http://www.ukbboy.info/PS-X-CHANGE-2...-download.html

Does anyone know how I should go about fixing this? And preventing it happening in the future?

Thanks