A few weeks ago OverwatchPD on twitter reported on a new aim hack called magic bullet.
When used properly it may be hard to tell if they are using this hack. However we now know that if used randomly it can kill through walls and possibly from the other side of the map.
It is unsure if it only works with Hanzo since he can produce a one shot kill. We will continue to investigate this and update this as a thread as more information becomes available.
Bilzzard should be able to shut this down quickly but until that happens, stay safe out there heroes.