The default settings shouldn't be cleaning anything untoward in the manner you've described. The default settings are as shown in the attached thumbnail.
However, you can disable the task.
Double-click the taskbar icon to open Security Center
Click Advanced Menu (bottom left)
Click Tools (left)
Click Start under the Task Scheduler section at the lower right
Delete the task there.
You can alter the Quickclean settings also by clicking the Start button in the Quickclean section at the top.
If you want to remove McAfee altogether then follow these instructions.
1. Uninstall all McAfee programs through "Add or Remove Programs" in Windows "Control Panel". (Programs/Uninstall a Program in Vista).
2. Use the MCPR tool, see this article: How to remove supported McAfee consumer products using the McAfee Consumer Products Removal tool (MC...
This will remove all McAfee remnants from your computer. (you must have Windows Vista, XP or 2000 SP4 to use this tool).