Ethical guidelines are more difficult to construct than ones for etiquette, but a few plausible ones are given here. Be careful with private correspondence. Someone is paying the bills. Don't post harmful instructions or information. Resource sharing services are not like anything else.
People depend on networks and conferencing systems.
Don't leave a security hole unfixed. Don't use security holes to cause damage. Don't quote text verbatim if it is copyrighted or covered by a restrictive license. Unless you have a philosophical objection to intellectual property, remember that breaking a copyright or license probably takes income away from the owner. When presenting an idea that originated with someone else, give proper credit, either by naming the source or by citing a formal bibliographic reference.