[quote=AlienBastard]
Although there lies a new issue; What about self replicating probes? A civilization that used such probes would be able to easily comb the galaxy in a mere 10 million years.
[/quote]

Freaky but I believe it has been done before in fiction.

A Solution of Mines:
- We are the aliens... we originated from aliens and their attempt to colonized earth was bombarding it with their species genetic materials which were modified with an evolution code i.e. our consciences is not random. Our home planet is patiently waiting for us to evolved sufficiently to establish contact. Ever wondered why christian bible say "God created us in his own image"? And other tens of thousands of references either referring to a God/Gods or being Gods ourselves?

P.S. These aliens are not capable of interstellar flight but they are able to anchor and catapult asteroids (which contains the genetic materials) to a selected destination.