My WordPress site was hacked

First post. This probably isn’t what the ‘Hack’ forum is for but I’m not sure where to start. Mods: please move to the appropriate forum. Anyway…

Click here for the site that was hacked. I was working on this a few months ago as a mirrored site of my main website. When I went back, I found that it had been hacked. I’ve had a couple of people look at it but they could not locate the hack. I know I can upload backups which I will do.

Does anybody have experience with this? Is there a file(s) I could upload that someone could take a look at?

Also, what measures would you recommend to prevent this from re-occurring?

Thanks for any help you can provide…