1) If you get a message, or see a posting on Usenet that seems like it should be shared with LOTS of people, **DON`T SEND IT** unless either you KNOW the message is true, you can authenticate their identity (through PGP or some other system), or you know the sender personally, and know they would have written this message. The more urgent it sounds, the more skeptical you should be. Even if you think it might be true, let someone else spread it.
2) If you really want to send it, **ALWAYS CHECK WITH THE ORIGINATOR** before forwarding it! This is the best way to tell a hoax or a prank. Just reply to the first sender, and ask them if it is true. If they can't tell you, then don't send it! Most pranks and hoaxes have forged headers and signatures, and when you try and verify the validity of the message, you will find that the address is not valid. Even if the originator is the prankster, and tells you to go ahead, at least they can be caught and dealt with. If this seems like too much of a bother, than it is not that important and you should not send it anyway.
3) If the message tells you to do something, especially if that something involves changing in your account or sending a file or message over the network, **CHECK WITH SOMEONE KNOWLEDGEABLE THAT YOU CAN TRUST**. Imagine you received a package in your real homes mailbox asking you to place your house keys in the return envelope provided, and mail them to a post office box. Would you comply? People fall for the computer version of this all the time.
4) If you see or get something that really makes you angry, remember *** YOU CAN'T BE SURE WHO SENT IT!!** It is very very easy to frame someone with an e-mail message or Usenet post. All someone has to do is sit at their computer when the victim is away from the keyboard. But hackers can be much more sophisticated. They can forge any message to make it appear from anyone.
5)Chain e-mail and Pyramid posts on Usenet are a scam, and most often, they are a crime. ANY SCHEME THAT INVOLVES REAL MAIL AT ANY POINT CAN BE ILLEGAL. If you forward one, you will be blasted with hundreds of angry messages in reply. But if you see one, remember that you can't really be sure who sent it!
6)Finally, note that when April 1st comes up, the Net will be awash in phony messages, forged return addresses, pranks, and general amusing nonsense. The best thing to do is to read them and have a good laugh. Baring that, ignore any message from anyone you don't know, and ignore any message from anyone that asks you to do something.