What do you do when a guy won't stop messaging you?

Hi! A friend of mind has a problem: there is a guy in her class and he sort of low-key stalks her. He won't stop messaging her the most random stuff. She really doesn't like it. How can she make clear she is not interested?
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+1 y
Thank you all so much for your advice. She is going to ignore him! :)
What do you do when a guy won't stop messaging you?
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