We would needs some more information in order to resolve this issue.
1) Please let me know what browser do you use and what is the version of your browser.
Internet EXplorer 8
2) Do you see this issue always or does this happen intermittently.
intermittent
3) What threads you where browsing when you saw this issue.
of course, it hasn't happened since this thread was started! 
4) Is it possible for you to get me a screenshot of the ad.doubleclick.net urls that you see in your browser back button.
If it happens again, I'd be happy to do so, that is, if you will tell me how to do this!
If you can provide us wiht the above information it can help us in resolving the issue.
Thanks,
Ibadmin - Quiltingboard Admin