Hello,
Just wanted to give everyone a head's up to watch their bags on the RER B coming from the airport. On 7/31 my wife and I were on the train which was getting quite full. Two males were switching cars at each stop. A female came on the train and started talking very loudly ( I couldn't understand) and was very close to my wife. We did not make eye contact. One of the males put his hand in between me and my wife when I saw the other crouch down and try to steal my backpack which was clamped between my legs. It was a sloppy attempt and he didn't get it. I spoke some obscenities at him and they left. I'm guessing the three of them were working together? Anyway, stay alert. That would have been a horrible way to start our trip! To be clear, this was the only instance. We rode the Metro extensively for five days and did not have any problems.