1.   Curiously, the aliens use guerrilla tactics, striking this city and that and then flying away, rather than invading.

2.   If the aliens used nanotechnology techniques now being explored by researchers, the JPL scientists said, they could construct the ultimate plague.

3.   But nobody knows for sure what channel might be used by aliens.

4.   Illegal aliens use Turkey as a stepping stone to enter northeastern Greece through the Evros river.