This is what the Cambridge Dictionary says (http://dictionary.cambridge.org/grammar/british-grammar/pronouns/someone-somebody-something-somewhere): Someone and somebody have no difference in meaning. Somebody is a little less formal than someone. Someone is used more in writing than somebody. Somebody is more common in speaking.

someone既可以指人也可以指物，但somebody只指人。 Mybe ,there is little differences between someone and somebody. Thanks.