Apologies if this is a pearoast but I've just come across this blog post warning of potential dangers found in free Wordpress themes. Now, I'm not wanting to scaremonger by saying all free wordpress themes are a problem. I'm just saying it's something to be aware of.
I personally haven't come across any issues with any free WP themes I've installed. Why You Should Never Search For Free WordPress Themes in Google or Anywhere Else - WordPress, Multisite and BuddyPress plugins, themes, news and help – WPMU.org