Two jurors have each been jailed for two months for contempt of court
One researched a case online, which is clearly against the rules. The other was silly enough to express his opinion of the defendant on Facebook.
Kasim Davey, 21, of London, said he had sent the Facebook message last December as a result of "spontaneous surprise at the kind of case I was on".
His posting - containing strong language and an offensive word - suggested he was going to find the defendant guilty, said BBC News home affairs correspondent Danny Shaw.
Davey's Facebook post: read: "Woooow I wasn't expecting to be in a jury Deciding a paedophile's fate, I've always wanted to Fuck up a paedophile & now I'm within the law!"
The judge at Wood Green Crown Court was alerted and Davey was discharged. The defendant, Adam Kephalas, was eventually found guilty of sexual activity with a child.
Davey told the High Court he was unaware he had been in breach of a formal order made by the crown court judge. He accepted he was not meant to discuss the case but believed he was only prohibited from using the internet to carry out research.
In their ruling, High Court judges Sir John Thomas and Mr Justice Sweeney said they rejected as "untruthful" Davey's contention that his message was not meant seriously.
They said it made clear to his Facebook friends "he would use his prejudices in deciding the case" and his choice of words "underlined his disregard of the duties he had undertaken as a juror".