hmm, if she/ he is using an internet cafe, since they might, considering how many times they've done this, they're probably sceptical, and innfecting the computer won't do them that much good either, replying is dangerous too. IDK, sending a virus would be fun, as would toying with them, or just sending one email to scare them off, I would suggest the later, as they may start bombarding you with messages if they don't get a reply. try telling the cops but, as others have said.
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