Pop Up Ads on My Blogs!

I have observed that my blogs have been getting this annoying pop up ads every time I view my blogs...it's so disgusting seeing them and mess my blogs up so that it occupies the whole page covering my blog. I wonder if anybody have been experiencing this too? My PC has a pop up blocker installed and it seems to be okay with other web pages when I browse on them. All my blogs are having them, and I wonder why...or else, I have to figure out if I might have some bad spyware links that are connected to me or some html that I have installed on my elements. I am also thinking if my message box is also connected with it. Gosh! it's tough finding which do these come from.