After an initial mission against the aliens, the site cleaning team are attacked upon their return to base with artifacts, It turns out alien technology has homing beacons built within it, fortunately at our current level of technology we can detect this locally (though not at as vast a distance as the aliens) and have found a way to mask the signature. However, whilst stocks off world artifacts are presently secure at our main base, the aliens may develop the ability to nullify our efforts going into the future and I would advise building a fortified science base, at the aside of our engineering, command and assault structures.