Tassadar captured the probes and brought them to Aiur for study. Using the khaydarin crystals, the protoss were able to read their thoughts... ‘Find
In addition, the protoss were able to determine the probes (and therefore the zerg) had been created by the xel'naga, which explained why the probes reacted so naturally to the crystal emanations.
When the zerg arrived in the Koprulu Sector these probes were also encountered by the Dark Templar. The Dark Templar tracked the zerg to Char and chose to test themselves against small groups of zerg.