rosie,the judgement about Norton is still out there and you will find ardent defenders and opponents of norton products, it sometimes appears like a fight good against evil...
Speaking from experience,it unlikely that some unexpected occurance like you described takes place again.
i have no answer about the "why it happened".
If you ever need to unistall a Norton product-Norton has its own unistall programme: click here
which you need to follow to the letter.