Creating a will online.?

I've seen and heard ads on TV and radio about creating a will online for a fraction of the cost a lawyer would charge. My question, Are these doents legal and acknowledged in a Court of Law. With all these scams going around is it advisable to do this, taking into account that a lot of important information will be furnished to a site whose legitimacy you know nothing about. Or would it be safer to just pay a lawyer and ease the worries.