This document from McAfee will assist you in resolving your virus issue Required Reading - Home User Assistance Malware Troubleshooting I would suggest that you try running the McAfee stinger scan which is mentioned in the document. After completing the suggestions in the document and you are still unable to download McAfee then try this free program http://www.malwarebytes.org/mbam.php
You should download this from a non infected pc onto a usb stick by renaming the download and installation files to something you can easily remember as virus and malware are written to self protect themselves. When you rename the files most of the time you can get the program installed as the malware no longer sees 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.
After you are sure you are all cleaned up try to install your McAfee software again. This links will explain things a little bit more in detail http://service.mcafee.com/faqdocument.aspx?id=TS100119 Please be sure to run the preinstall tool mentioned in the link.
Just wonder if you have a order reference number or some type of authentication information concerning the free software from Cox? I would certainly thing that Customer Service should be able to help you out in that area.