PGP (Pretty Good Privacy) was used as a email encryption program – but now it’s no longer freeware. I recommend GnuPG, which does the same thing but is free. This site will lay out how to download and use GnuPG4win, which is GnuPG that works on Windows. Here is the link for Mac users, and here is the list of all supported systems. If you don’t trust my links, you can go to http://gnupg.org to check it out.