If it's malign there's really nothing we can do about it. A technology that can traverse the distance between solar systems is so far outside of our technology that it might as well be magic, and our current level of technology is already adequate to obliterate all life on the surface of the Earth. If you have power to travel interstellar distances the power to obliterate all life on a planet with no warning is trivial.
Ironically we might be in less trouble if they have FTL technology, since that might not require quite the outrageous level of technology you would need to do the journey with the physics that we know. The rocket equation is a harsh mistress.
Ironically we might be in less trouble if they have FTL technology, since that might not require quite the outrageous level of technology you would need to do the journey with the physics that we know. The rocket equation is a harsh mistress.