• Computer viruses are a very real threat to any computer system. Viruses and other malware can infect a computer either through corrupted email attachments or through malicious websites and result in a number of performance problems. Norton Anti-Virus and McAfee are two of the most commonly used antivirus programs on the market and while they are generally effective against threats, they can create problems if you try to uninstall them from the system.
  
  

Program Interference

• Norton and McAfee can both be resistant to being removed at times and can cause compatibility issues with new security software when you try to install it. You may believe all of Norton or McAfee has already been removed and then receive a notification that your new security software cannot install due to Norton or McAfee being present. This is usually due to a fragment of the Norton or McAfee program remaining and preventing new software from replacing it. Go through the uninstall process again and then immediately reboot your system before attempting to install any new programs.
  
  

Registry Changes

• While the Windows utility for adding and removing programs generally works well at eliminating all traces of a program you want deleted, Norton and McAfee can frequently cause changes in your registry that results in the computer consistently looking for those programs and then reporting errors when they are not found. Norton, in particular, is known for this and your registry needs to be repaired to eliminate the instructions for Symantec, which is Norton's parent company, or McAfee. Symantec has started offering its own uninstaller to automatically repair these registry issues but reviews on its effectiveness have been mixed.
  
  

Multiple Pop-up Warnings

• Security software is generally resistant to being deleted. As a result, both McAfee and Norton will flash various warnings as you are in the process of deleting them from your system. The warnings will claim your system is at risk and your computer will be unprotected against viruses or compromise. While it is true that computers without any security software are at higher risk against virus infection, most people delete a security program so that a new one can be installed, so you can ignore these warnings and proceed with the uninstall. You always want the old version of Norton or McAfee removed entirely before attempting to install a new antivirus program, especially if the new software is from a rival company that Norton or McAfee won't recognize.