It's not that unlikely, and it happens. Some insider at a low level doesn't have access to the info but can find out who likely does and all of a sudden that person comes home to a few people in the house threatening to kneecap their wife and kids unless they turn it over. Hell, the witness protection list itself was leaked a decade ago, not even just a specific individual. A federal marshall was also charged with giving info on people in witness protection to mobs. You'd probably spend the $5m on therapy from having to constantly look over your shoulder for the rest of your life. Also what if they give you a shit name like Colin.