Joanne Fraill, the juror who contacted a defendant on Facebook, has been jailed for eight months.
The Lord Chief Justice, Lord Judge, passing sentence, made plain that the punishment was exemplary and designed to deter future jurors from conducting online research or using social media to contact defendants in trials.
The judge said that although Fraill was not involved in an attempt to pervert the course of justice, "the sentence is intended to ensure the continuing integrity of trial by jury."
Fraill, a mother with three step-children, wept when the verdict was announced.
The judge, in a written ruling stated: "Her conduct in visiting the internet repeatedly was directly contrary to her oath as a juror, and her contact with the acquitted defendant, as well as her repeated searches on the internet, constituted flagrant breaches of the orders made by the judge for the proper conduct of the trial."
Fraill admitted contacting a defendant in a drugs trial, which caused the prosecution to be abandoned.