Sometime it is neccessary to prevent site or perticular page opening in IFRAME. To do that use following code in page or site. (Someway every page on site).
if(top != self)
top.location = self.location;
If some page written above code and still you want to open that page in IFRAME. You need to use following syntax. This is only supported in IE.
<iframe src="write your url that contain above code." width="500" Height="500" security="restricted">
If any one have firefox solution for this please inform me.