As sloebertje has ably pointed out, white chocolate is not really chocolate at all, for it doesn't contain any chocolate liquor, unlike the real thing. White chocolate is made from cocoa butter, the naturally occuring cream-coloured fat that results from the processing of cocoa beans, mixed with sugar, milk solids, lecithin (an emulsifier), and vanilla. If the label does not list cocoa butter as an ingredient, don't buy the product; it's made from some other kind of fat than cocoa butter, thus severing white chocolate's already tenuous connection with that gorgeous dark elixir, chocolate.
Because it contains milk products, white chocolate only lasts about 8 or 9 months under ideal conditions (tightly wrapped, in a cool dry place); milk chocolate, which also contains milk products, lasts longer because cocoa solids contain something - as yet un-identified compound - that prevents the dairy ingredients from going rancid. White chocolate, like all chocolate, must be melted very slowly over low heat - preferably in a double boiler over simmering water - to keep it from scorching and clumping.
I am curious as to the origin of white chocolate, for I don't remember it from my childhood, but I have been unable to determine it in spite of diligent searching. Odd. | 
