Myloki

Humanity doesn't know their name. Doesn't know their goals. Doesn't know the full extent of their powers. Doesn't know their homeworld. In fact, humanity doesn't even know their name. The name Myloki was chosen simply so their enemy could be called something rather then just "the enemy". All humanity does know is that the Myloki are inimitable to human life. For whatever reason, humanity has earnt the ire of the Myloki, who engaged in both an open "invasion" and a more subtle infiltration and conversion of humanity. Through the use of bombs and other terror tactics, the Myloki defeated and humiliated humanity and it's defenders. For whatever reason, they stopped their attacks after a bomb was detonated on the moon, at their nominal 'base'. However, the devastation left in their wake left a human race on the verge of extinction, cities in chaos and the defenders desperate to ensure that the Myloki could never return and in terrified apprehension that at any moment that might.

Biology
As far as the Doctor is aware, Myloki are incomprehensible. Even to him as a Time Lord. However, the way he describes them, as being something so totally opposite to anything he's encountered before is eerily similar how the entities in Planet of Evil and Zeta Minor are described. It's possible that there is a link between the Myloki and the entities beyond the matter/antimatter boundary.

Life Cycle
Unknown, and possibly unknowable.

Technology
Whether or not what they create is a result of their own technology or simply reegineering human technology is unknown.

Trivia

 * The effect a Myloki "searchlight" has on the Earth creates matter very similar to the 'forest' on Zeta Minor, down to the haunting animal sounds and feeling of oppression, again hinting at the possibility of some sort of link between the two.