von Neumann probe

What kind of rules should our probe obey

von Neumann probe designed by human race could be programmed to follow roughly these kind of rules. Maybe probes of some other civilizations could use this kind of rules. At least if that civilization consist of semi-carnivorous species living in social organization.

Do not let anybody reverse engineer you or your probe relatives

If somebody manages to capture and reverse engineer our probe they could develop much more effective ways to combat our probes. They would now the details of our weapons, our negotation principles and other such things. In the worst case, our "software update" protocol could be reverse engineered, should we use one. That could mean somebody can rewrite the behavior patterns of every single existing and future probe of ours.

If the threat of capture can't be completely neutralised it might be good idea to build several slightly different probe models. Therefore it would be less likely to end up in situation where our probe armada is entirely useless against other probes. Also, possible attack planners couldn't be sure if they have enough information for attack.

Every probe should be equipped with auxiliary scout probe that can be sent to habitated areas. This probe should be unarmed, because there might be situations where other probes or inhabitant of some area allow only unarmed probes to perform inspections.

When you encounter a probe of unknown origin make sure it works under morally acceptable principles

When you encounter unknown spacecraft try to communicate with it at least via radio and visually.

http://en.wikipedia.org/wiki/Lincos_%28language%29

If it fails to communicate with you start to follow it. If it does something that is morally inacceptable (for example mining a habitated planet) try to quarantine it. If that fails use any means necessary to stop it.

If communication is established tell it your mission and ethic principles and listen what it has to say about it's own. If your princinples differ try to negotiate with it the way you are programmed to. If you can reach consensus the matter is settled . If it turns out that the spacecraft is working under clearly immoral principles, propose that you both retreat, declare war and tell others about it. After that you and your sister probes are enemies with the newly encountered type of spacecrafts.

After you have sufficient information about the new spaceship share the information that you have gathered with your sister probes and other probes you consider trustworthy.

However, be aware that some probes might try to cheat you and work under different principles that it announced to you. If this is detected, take appropriate measures depending the severity of a breach.

Was Wow! signal communication between probes?

Keep your eye on planets, moons and asteroids so that no one can manufacture aggressive von Neumann probes

In case some civilization(s) actually builds an aggressive von Neumann probe it must be hit every place possible. Only machine capable of this is another von Neumann probe.

Ideally the aggressive probe is destroyed before it leaves the place it was built.

Weapons inspectors, interplanetary Hans Blix if you will. 

Do your best not to reveal your existence to young civilizations

See some reasons here

Send every 10000 copy of yourself to the vicinity of Earth to report what you have found and experienced.

This is necessary for humans to determine if the their probes are and have they detected any hostile probes and can the their probes handle the situation. It is also important for collecting scientific data from visited planets and moons.

Another possibility could be transfering collected information via radio or similar device. The question is, however, is it possible to create fast connection enough for large quantities of data? Especially if transmission is disguised as natural radio source in order to hide it from those that might use it for wrong purposes. And of course in order not to shock young civilizations that are unaware of others.

Do not steal resources

Never mine more resources than necessary for your mission. Prefer materials that are far away from any kind of life.

When you encounter probes of foreign origin, negotiate with them how much local resources each probe family is allowed to consume.

On the other hand, according to Freitas:

"The total mass of probes needed to explore even the entire Galaxy is astonishingly small. If each self-replicating probe, mass fully-fueled about 10¹⁰ kg [30], makes 10 replicas during each of 11 generations, enough to span the entire Galaxy [32], that is 10¹¹x 10¹⁰ kg = 10²¹ kg or about the mass of Ceres, the largest known asteroid. If the Solar System carried the burden of manufacturing all 10¹¹ probes to explore the entire Galaxy, how could we know if one Ceres-size asteroid had ever been removed from the Asteroid Belt?"