Because the WIMPs are moving around in the halo in all different directions, the way they crash into Earth will be different each time. For example, a WIMP moving completely the opposite way as the Earth will create the largest change in energy, whereas a WIMP going in the same direction as the Earth will produce a smaller energy. This makes it much harder to distinguish WIMPs from background noise because the energies can vary significantly. (4, 6)

One of the experiments trying to combat this problem is DRIFT. DRIFT uses a container filled with a heavy gaseous element and as the WIMP moves through the the gas, it will scatter the atoms of the gas. From there, you can find the path taken by the WIMP. This allows physicists to be more confident in detections. So far, DRIFT has not detected any WIMPs. (6)