Anionic energy

From Memory Alpha, the free Star Trek reference

Anionic energy is all that was left after criminals from Ux-Mal were separated from their bodies and exiled on the barren moon of Mab-Bu VI.

The criminals could superimpose their neural pattern over those of non-suspecting Humans, like the crewmembers of the USS Enterprise-D. The anionic energy could only be detected by a comparing the transporter ID logs of the affected crewmembers.

Only great amounts of pain, like a plasma shock could drive the aliens out of the host bodies. The anionic energy was furthermore very vulnerable to certain magnetic flux densities found on the surface of the moon that could be imitated by ionogenic particles.

After freeing the hosts from the energy, it could be contained by a neutrino field. (TNG: "Power Play")