WHY NOT TO USE ANY VERSION OF PGP:

PGP _used_ to under a fairly liberal software licence, and its only major
problems were (1) patent restrictions on the RSA code, and (2) USA export
restrictions.  Then, its creator, Phil Zimmerman, sold his copyright (and
business) to Network Associates, Inc., who have added further restrictions
over time.  The current NAI version, 6.51, is available in binary form
_only_.

The generally-superior "international" ("pgpi") 5.0 version
is available at ftp://ftp.pgp.net/pub/pgp/pgpi/5.0/ (source and 
sundry binaries).  That was the last version that could reasonably
be used internationally -- and IT had problems in that area (including
patent restrictions that will render its RSA-algorithm illegal in the USA until
September 20, 2000, when that patent expires).

The latest NAI pgp 6.5.x version, _issued in binary form only_, is also 
available from ftp://ftp.pgp.net/pub/pgp/.  Commercial use (among other
things) of that version is prohibited.


Summary:

The cumulative effect of different, poorly-compatible USA ("pgp") vs.
international ("pgpi") versions supporting varying algorithms, patent
restrictions, import restrictions, and the disappearance of source code from
the NAI versions has rendered PGP functionally just about useless.


Good news!  A genuinely free replacement, GNU Privacy Guard (gpg, also
called gnupg) has been released and is being widely adopted.  It completely
replaces PGP.  Advantages:

-- standards-compliant (RFC2440 aka "OpenPGP")
-- no patent encumbrances
-- no export restrictions
-- licenced under the GNU General Public License
-- decryption/verification is a superset of pgpi 5.0

http://www.gnupg.org/              GNU Privacy Guard home page
ftp://ftp.gnupg.org/pub/gcrypt/    Primary ftp site
http://www.gnupg.org/mirrors.html  List of ftp mirrors

Also available: a large variety of add-on software.  See:
http://www.gnupg.org/download.html