i wouldn't touch norton with a bargepole even if it was free,it's one of only two antivirus programmes ive come across that has actually made hardware such as a floppy drive or memory malfunction - oh the other programme was macafee ,i wonder how many people had already guessed that.
norton are typical of those companies who like to blow their own trumpet,usually a crap product that relies upon hype from numpties such as those who work in places like pc world to con people in to buying it.
same in its workings,because it looks big and gets in your face a lot people think it must be good,try one of the good free ones,they run nice and quite in the background,dont hog half your memory, just see how much quicker your pc runs