Defamation can be a crime as well as a civil wrong. Criminal defamation occurs when one purposely communicates to any person, orally or in writing, any information which he or she knows to be false and knows will tend to expose any other living person to public hatred, contempt, or ridicule.
The following is a State Statute (Montana) defining Criminal Defamation:
Mont. Code Anno., § 45-8-212 Criminal defamation.
(1) Defamatory matter is anything that exposes a person or a group, class, or association to hatred, contempt, ridicule, degradation, or disgrace in society or injury to the person's or its business or occupation.
(2) Whoever, with knowledge of its defamatory character, orally, in writing, or by any other means, including by electronic communication, as defined in 45-8-213, communicates any defamatory matter to a third person without the consent of the person defamed commits the offense of criminal defamation and may be sentenced to imprisonment for not more than 6 months in the county jail or a fine of not more than $ 500, or both.
(3) Violation of subsection (2) is justified if:
(a) the defamatory matter is true;
(b) the communication is absolutely privileged;
(c) the communication consists of fair comment made in good faith with respect to persons participating in matters of public concern;
(d) the communication consists of a fair and true report or a fair summary of any judicial, legislative, or other public or official proceedings; or
(e) the communication is between persons each having an interest or duty with respect to the subject matter of the communication and is made with the purpose to further the interest or duty.
(4) A person may not be convicted on the basis of an oral communication of defamatory matter except upon the testimony of at least two other persons that they heard and understood the oral statement as defamatory or upon a plea of guilty or nolo contendere.