Blogger in need of assistance...

I need some help from my readers... Without my permission or knowledge someone inserted a pop-up ad into my blog. I don't know how and/or where this was done. It brings up a pop-up for either blonde jokes or high arcade scores. Does anyone know how to get rid of this? I already went through the process of deleting my cookies and entire internet history. I also ran Ad-Aware and Spybot to no success.