Copy/paste of info I posted to /r/EndlessSpace:

If UC1 and UC2 both have sanctuaries in a system, they will always know of the others, regardless of the system cloak level.

If UC1 hacks a system, they will discover any UC2 sanctuaries at the destination, but cannot destroy them on this hack. If there is still room for another, UC1 may place a sanctuary that UC2 will immediately detect or cancel the finished hack for a bandwidth penalty. If there isn’t room (and nobody else colonized the system for real), the hack is cancelled without a penalty.

If UC1 plants a beacon on the node where UC2’s Nexus sits, the beacon will fail and UC1 will detect UC2, regardless of system level.

If UC2 relocates to a node with a beacon from UC1, the Nexus is not revealed unless UC1 tries to activate the beacon. In which case, the beacon will fail, all existing UC1 beacons are destroyed, and UC1 will detect UC2, regardless of system level.

If UC1 successfully invades UC2’s sanctuaries, UC1 can choose to destroy them and relocate the Umbral Choir pops back to UC1’s Nexus (plus a 50% hack boost in nearby systems)

If UC1 manages to plant sleepers/sanctuaries on UC2’s Nexus, they are lost/destroyed if UC2 successfully transmigrates. Any created backdoor will remain on the special node; it will not follow UC2’s Nexus.

The Umbral Choir will immediately know if any of their systems are detected, and checking the system cloaking level will show everyone that discovered it. The UC won’t get a pop up, but any UC hacks originating from and traced back to a sanctuary system without a friendly backdoor will also reveal the sanctuaries to the tracer (but anything along the way is safe from detection).

Very interesting. Thx