The area of law most implicated by that type of conduct is "defamation of character", a cause of action which is generally defined to include "libel" and slander".
What Are Defamation, Libel and Slander?
Generally speaking, defamation is the issuance of a false statement about another person, which causes that person to suffer harm. Slander involves the making of defamatory statements by a transitory (non-fixed) representation, usually an oral (spoken) representation. Libel involves the making of defamatory statements in a printed or fixed medium, such as a magazine or newspaper.
Typically, the elements of a cause of action for defamation include:
A false and defamatory statement concerning another;
The unprivileged publication of the statement to a third party (that is, somebody other than the person defamed by the statement);
If the defamatory matter is of public concern, fault amounting at least to negligence on the part of the publisher; and
Damage to the plaintiff.
In the context of defamation law, a statement is "published" when it is made to the third party. That term does not mean that the statement has to be in print.....
source - http://www.expertlaw.com/library/personal_injury/defamation.html