Always show extension for known file types!A recent study showed that over 60% of virus or worm infections are caused by the users negligence when opening files received as attachment to an email, by some instant messaging client or a download software. It's a very old method that still works! A virus renames itself as "picture.jpg.exe", use a picture icon and some unsuspected user is fooled!
According to last years' statistics, nearly a third of the World's PCs were infected with viruses. Don't add yours to the count. Keep your data private, use Norton 360. Be smart. Stay protected!