Hacker help

I am constantly having issues with someone hacking my wordpress site. Normally they just get in and change the front page and my log in information. I remove the front page files and then go into my MySql and delete the user they create and get access to my wordpres admin again.

This time they could not change the front page. They were able to put some file somewhere on my site though. If I type in the url to my site and then anything after that that isnt part of my site I see the hackers page. The problem is I can not find a file that they have edited to make this show up.

Is there a way for me to find the hacked file and how do I keep this from happening so often? I have a very strong password for my login and my cpanel.

Thanks for any help.