If the age of consent in NY is 17, but the age of consent in another state is 16, which applies?
What if it is over Skype, of ChatRoullete etc?
Cyber-sex is not sex and the age of consent is not the issue. In fact in NY at least a 18 year old and 15 year old can have sex and it isn't a sustainable crime, but if the 18 year old has cyber sex with the 15 year old, he is guilty of both Federal and state crimes in both her state and yours. Again if they aren't at least 18, stay far away.
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