a strange popup window opens in website

i have a games website. in that there are more than 4000 flash games available.

Now my problem is in my website i am getting a strange popup window wheneve开发者_StackOverflowr i first open up my web site in a day that pop up appears with sometimes google, sometimes yahoo sometimes and somee other sites..i dont know how the popups are coming..

i havent added any code for those kind of stuff to open ...can anyone tell me how its happening..

My website is startonlinegames.com

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If your website has ads or simular things on it which are derived from a url or external javascript, those can add the popup to your website.