I used to carry a number of security software programs but I have decided now to carry only the two I beleive, based on my experience, are the best.
For the most effective, unintrusive protection for your PC, I recommend ESET and Kaspersky products.
** Remember always to fully uninstall any Antivirus before you install a new one. Any remnants of the previous Antivirus will conflict with your new antivirus and often cause serious problems for your PC. See my section on how to remove Norton. Follow the procedure there to remove your previous antivirus before you install your new one.**