a good way to defend against such probe team actions is to have a "defensive" probe team in a base. The cheapest one, early in the game is probe team on infantry chassis, 0-1-1. It costs only 2 rows of minerals. Because it is supposed to be stationed in a base, it does not need faster rover chassis, on occasion it can still perform some actions in the vicinity of a base, more far away, if along a road. Also, later in the game, such infantry probes can be elite, so will have +1 move point.
There is more to probe teams, you can equip them with various armors, reactors, that will influence cost. It's actually quite fun to design such units.
Probe teams fights is yet another aspect of the game - they use morale to determine their strength.
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And something else about probe team action:
- zone of controls - there is cloaking special ability allowing regular military units to move inside zones of control of enemy units. This special ability comes late in the game, but in early game probe teams can be used to do it. They can move inside zone of control anyway, so you can send one tile a probe team first, then according to the rule that you can enter a tile where you have already at least one unit, a regular unit can enter that tile too. Good way to sneak by enemy sentinels, which otherwise would block passages due to zones of control.