I've moved your post to our VirusScan area for Home Users. Hopefully a product expert can help you soon.
Could you please provide the following information so that we could help you with our best here;
What is the computer’s operating system ?
What is the RAM size of the computer ?
Do you have any other security software installed in the computer ?
Do we receive any anonymous pop ups in the computer ?
5 hours to do a full scan? You are lucky! Mine takes 8-10 hours if I let it run at night. I use to tell my family that McAfee was better than Norton but I am increasingly becoming scepticle. I have had more sucess stories by manually running Anti-spyware with the Yahoo Toolbar and Microsoft Security Essentials (MSE) than with McAfee which is running full-time on my machine with "full realtime" protections and semi-nightly full scans. MSE found win32/alcan D, win32 alcan B, and win32/troxen!rts on this week. As I type, I am running their Windows Live free online scanner (http://safety.live.com) and it has detected something (unsure until it completes). What is my McAfee software doing?! Other than using up resources and emptying my wallet once a year!
Essentially if you disable both you have turned off the McAfee security suite. That's why it keeps coming on when you launch the program. One or the other should be on. If you choose not to do this, then shut off the program, then turn it on at a regular interval and scan your machine. You will get virus this way though.