I was pick pocketed twice; first time I caught the Roma woman by the wrist at Nation. Second time I lost my wallet from a zippered front pocket at Anvers on M2 by African dudes that I had to squeeze through. Nation seems the worst, saw several flagrant fare cheats at the styles, one reached over the exit doors and banged the bar to open it. The others were juveniles reusing the same ticket.
Word of advice - if the train is really packed, wait for the next one if you can. The teams may pack the entry to get their chance to rip you off.