PGP (Pretty Good Privacy) is the best tool available to counteract forgery. Using a so called ``public key encryption'' mechanism, PGP allows one to ``sign'' a document to prove that he/she really wrote that document. A PGP signature will also confirm that a document hasn't changed since it was signed. The only known way to forge a PGP signature is to capture a secret PGP password that only the signer knows.
If somebody signs a email or news posting using PGP, and you've verified the PGP signature, you can be pretty sure that the note was sent by that person, and you can be sure that the note hasn't been modified.
Look at the man page for ``pgp'' to find out more about using PGP. In the HSEAS we provide a special command pgp_init to help you set-up PGP. Also, see the PGP FAQ in the appendix of this document.