The High Templar Tassadar, accompanied by his renowned Templar expeditionary force, foudn a number of small biological constructs floating near the borders of Protoss space. Upon close inspection, Tassadar deduced that the rather nondescript alien organisms were in fact deep space probes. Although Tassadar could not discern their point of origin, it was clear that they were heading towards the Koprulu sector of Terran colonies.
Tassadar brought the living probes back to Aiur for immediate study. The strange aliens were unlike anything that the Protoss had ever seen before. The respective physiologies of the probe were apparently engineered for deep space travel and reconnissance. In an attempt to discern their primary quarry, the Protoss focused the energies of the Khaydarin Crystals through the tiny minds of the probes. The Protoss were shocked to discover that the alien probes responded quickly and naturally to the powerful energies of the Crystals. Their shock was garnered from the fact that only creatures born of the Xel'Naga's proto-genetics could properly process the energies of the great Crystals. More alarming was the vague thought stream that kept repeating, over and over, through the tiny brains of the probes; 'Find Humanity'... 'Eradicate'... 'Learn'... 'Evolve'...
The Protoss speculated that the probes were the harbingers of a bold new threat to their section of the galaxy. If the creatures were engineered with Xel'Naga technologies, they would be very advanced and extremely powerful. It seemed clear to the Protoss that this new race constituted a palpable danger to all living beings, and that wherever the greater bulk of the race was, it must still be searching for the unsuspecting colonists.
The Protoss began to send out advance scouts to scour the surrounding space-ways for any sign of the alien invaders.