Web surfers spoiled a national promotion by General Motors that was intended to gradually reveal a secret message.

Under the campaign, which is about half completed, each day a billboard in a different part of the country divulges a word (or a punctuation mark) in a message. A billboard in Arlington, Tex., for example, says "you." One in New York City shows a period.

The billboards also promote the Web site www.findthemessage.com, on which GM explains that it created the campaign to spread "a message so important we need the whole country to tell it."