I'm seeing ads on webpages?

I'm seeing advertisements on webpages that don't even have a script in the source. It looks almost like a Windows Live Messenger alert box (sign in, new message, etc). http://i35.tinypic.com/akbpd1.png I think I've heard of something like this before, and the cause was some virus that was implementing ads on... show more I'm seeing advertisements on webpages that don't even have a script in the source.

It looks almost like a Windows Live Messenger alert box (sign in, new message, etc). http://i35.tinypic.com/akbpd1.png

I think I've heard of something like this before, and the cause was some virus that was implementing ads on pages you browse? Is that true?
Update: I don't look at porn. I'm seeing these ads on pages like google.com and smashing magazine.
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