The question is how big is the risk – because, of course, it will never be demonstrably zero. It’s impossible to prove something doesn’t exist, even when it’s as intangible as risk. Therefore, it only makes sense to look at the factors that decrease the risk – at what makes it unlikely that hostile aliens could find the location of Earth and invade.
Difference. The likelihood of Earth being a useful target is low because few planets are even similar to, let alone the same as, another. The aliens would have to find the Earth to be the most viable source of something valuable to them, even though their planet is vastly different from Earth. Their needs, through evolution, will match what exists on their planet rather than here. Volatiles (hydrogen, methane, etc.) are easier to gather from gas giants and moons, and metals are easier to mine from asteroids and comets.
Interstellar separation. Our current knowledge of physics implies that nothing can travel faster than light, and anything that does approach that speed suffers massively from the effects of time dilation. Therefore, either the aliens take actual tens of thousands of years to travel from star to star, or time dilation makes it a one-way trip because if they return to their home planet, it’ll be tens of thousands of years older than when they left. The distance they must cover is mind-bogglingly huge, and the trip is expensive, dangerous, and long – unless they’ve cracked the lightspeed barrier, which is very unlikely.
Intelligence. With great intelligence comes great insight and curiosity…and the effort towards scientific advancement. These things tend to replace or at least greatly diminish the basic instincts of fear, suspicion, and violent tendencies.
Location. Of course, even if aliens find our planet useful, they could be on the other side of the galaxy rather than anywhere near Sol. Likely, they’ll never find us in the galactic forest or through all the clutter of gas, other systems, and so on.
Purpose. For what purpose would they be hostile? There is as much chance they’ll be indifferent or helpful. Why travel across interstellar distances just to pick a fight?
Simultaneity. These aliens need to exist in the time we do. The universe and our galaxy have great age – a long past covering billions of years and an equally long future. We have existed for a mere eyeblink of time. The aliens probably won’t arrive until long after we leave if we ever learn the secret of getting around from star to star as they do. Either that or they arrived before we existed and moved on.
With all those factors counting against invasion, it seems there’s a very low risk.