My friend asked me to help him look into this blog which was running Adsense and he noticed that the Adsense Ads looked a little weird.. it wasn't his Adsense ID - someone has switched his Adsense Pub ID to theirs..
So I looked around and found this WP Plugin "Adsense Integrator" was the problem.. look into this plugins code in the file and you will find that this author has inserted this Adsense ID to switch between his id and yours...
If you've been using this plugin (DELETE IT NOW!!!) and getting ripped off by this person, I would suggested you report him ASAP!!!
Here is the link to Google to report this scumbag...
You should also report this to WORDPRESS.ORG
Best of luck!