Help me!!!

Someone who understands networking at the detail level and who can interpret the RFCs involved, one of which is this one rfc792, could much better explain this I'm sure. The best I can do is mention a few things I think are true based upon some observations and some reading (so techs please excuse me for some incorrect technical terminology )...

I believe the original intent was that the gateway to the host being pinged would return a host or destination unreachable message to the source, (the host issuing the ping), if the destination host was unavailable. (A rather useful service, I believe.) But with all the changes, hacks and stealthing going on today on the Internet, I don't think you can count on this any longer. Especially given the more dramatic changes (restrictions) the network providers have been implementing lately to combat all the silly worm related network traffic.

So, I would guess that whether you get some form of unreachable message or not, given what's going on today, is pretty much a flip of a coin. I don't think you can rely on it in all situations in order to figure out if a host is really there or not.