Check out the data from this paper, starting about 1/3 of the way down
the screen:

http://www.coseti.org/lemarch1.htm

Incidentally, if we exploded in space all the nuclear weapons humanity had
in 1990 (about 50,000), the x-ray signature could be detected out to about
190 light years. The famous Sakharov promoted a similar idea seen here:

http://lnfm1.sai.msu.ru/SETI/eng/articles/sakharov.html

As I said, there is not much to worry about with an alien civilization attacking
us because there is not much we can do at this stage of our society.

If the aliens do not possess a means to leave their world, then the only
threat they offer is to themselves. Carl Sagan suggested that hostile
societies probably wipe themselves out before making it into the galaxy.

Perhaps a bit of wish fulfillment, and it also does not take into full account
what might be good or evil to an alien society. Missionaries thought they
had nothing but good intentions for the native folk they were coming to
"save", but often ended up destroying their way of life, if not the people
outright.

If they can navigate the stars and are still "hostile", they have about 400
billion stars across 100,000 light years to search for us. Would it be worth
the time and resources to do so? Maybe if they think in very long terms
and predict us as a threat in the next few millennia to their galactic plans,
then maybe.

If these hostile aliens do want to get rid of us for whatever reason, all
they need to do is launch a starship at relativistic speeds right at Earth.
The kinetic energy will be more than enough to kill just about everybody.
No need for an expensive invasion fleet or fancy weaponry. And if they
do launch such a killer ship, we won't ever know what hit us.

Or perhaps the more likely scenario is that they are focused on their
own immediate concerns, just like us, and can't be bothered to deal
with or even look for a species that has only been to its natural satellite
once and won't do so again for another two decades, with just a few
probes that will barely make it outside their solar system before expiring.

And I will say it again: No matter how many restrictions are in place or
how fearful and ignorant most of humanity is, a few will always find a
way to break free of their confines and set off for the wider Universe.
Other species may do the same. We are going to meet one - unless the
galaxy really is empty except for us - so we better get ready, and I do
not mean by hiding under our beds and covering our ears.