Facial recognition
The judge can ban them from finding out the juror's name and searching for them, but if they can get pictures of them they might be able to use facial recognition to find out who they are.
Might be something more up Facebook's alley today, but if 'face unlock' became a popular feature in Android, then Google would be able to figure out who over half the potential jurors were. They could simply find a reason to excuse the ones they couldn't identify, leaving a jury packed with people whose names they knew but the opposition didn't, and they'd have a big advantage in every trial!