Why are pop up windows opening on my computer?

[shredder]

About 15 times a day two new browser window suddenly open...They are spam telling me I won or trying to get me to download something.  Here is the URL of one that opened.

http://media.defaultimg.com/images/defaults41/approved/404.html

There must be some spy ware in my system.  Why doesn't my McAfee remove it during the scans?

[Peacekeeper]

This link may assist you in removal of the virus you have on your  computer

Required Reading - Home User Assistance Malware Troubleshooting (http://community.mcafee.com/docs/DOC-1294)

You  might also try to run Malwarebytes http://www.malwarebytes.org

and  SuperAntispyware http://www.superantispyware.com

both  programs are free and catches a lot of stuff. I suggest you download these to a  usb stick on a non infected PC and rename the download and installation files to  something you can easily remember as virus and malware are written to self  protect itself so by virtue of renaming them the virus will not see them as a  threat. After installation check for the latest updates and run the program and  let it clean everything it finds and reboot the computer. Next step is to do the  same for the other program.

Try booting into safe mode and perform these  procedures. I see you have already tried MBAM and Spybot but maybe safe mode  will get you cleaned up.

Let us know how this works for you.