Jurors’ inability to refrain from posting information about court trials on social media sites like Twitter and Facebook poses a serious threat to the judicial system, with such behavior threatening mistrials and overturned verdicts, according to a recent report in the Wall Street Journal.

In one high-profile case, an accused murderer’s conviction was thrown out after a juror was found to have tweeted about the case on Twitter throughout the trial. The accused on trial, Erickson Dimas-Martinez, was found guilty of murder in March 2010 by an Arkansas jury and sentenced to death for the robbery-murder of a teenager. But in December, the Arkansas Supreme Court set aside the verdict and ordered a new trial – saying a juror who tweeted about the case was guilty of juror misconduct.

In other cases, jurors have been chastised and even held in contempt for “friending” defendants or plaintiffs on Facebook. And this month, a state appeals court in Sacramento, Calif., will hear a motion from defense attorneys in a gang-beating case asking to overturn verdicts against their clients in light of a juror posting information on Facebook during the trial.

Judges typically request that jurors refrain from posting online information about cases they are hearing. The judges are concerned about what jurors may say when they tweet or post, fearing that the jurors may reveal a bias about the case or disclose information that has not yet been made public.

But, while courts routinely impose social media bans on jurors during trials, it is proving quite a challenge to enforce these bans. The Wall Street Journal observes: “At a time when authorities can’t even stop some people from risking their lives by sending text messages while driving,” getting jurors to restrict their social media use is proving  a particularly difficult feat.