f9a0008e_Libel_Lawsuits_and_Information__Question
[Answer] Depends on the case and on the jurisdiction. You can read about a few anonymous Internet defamation cases, here and here. [Question] 
Does an ISP have to turn over the name of an anonymous poster who is being sued for defamation?
Online Defamation Lawyers: Online Libel Lawsuits and Information
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