1 scenario, 16 small ruins, 68 medium ruins and 28 large ruins consisting of minable buildings that contain various resources and the odd biter here and there.
Just as title says, structures from other mobs spawn biter ambush. For now I can say that Large Warehouses from "mods.factorio.com/mod/Warehousing" and some buildings from "mods.factorio.com/mod/Age-of-Production" do, not tested much yet.
ok I changed a few entries in 1.0.2 so I think it should be fine to mine other houses now without the ambush, I have to admit this was quite amusing to me, thank you for the report!