Seasoned users of electronic mail equate sending important data through a public on-line service with dispatching secrets on a postcard. Users transmitting privileged information electronically have no foolproof way to protect against a document's being peered into, altered, or forged. Can it happen? Already, Big Brother censors at CompuServe, America Online, Prodigy, and other services admit to editing or deleting bulletin-board entries. Similarly, any system operator on the Internet can pry into E-mail, and determined hackers can breach E-mail boxes. Or a mischievous third party could simply pretend to be a document's author.

To allay apprehensions, encryption software is available that breaks down an ordinary E-mail message into unique code, allowing only recipients with a special key to reconstruct it. And appending a digitized "signature" verifies that the sender was the true originator. Here are two popular offerings:

· ViaCrypt PGP, a patent-protected commercial product offering encryption and signature capabilities for both text and graphics applications. Its prices are $99.98 (DOS version) and $119.98 (Windows version specifically for CompuServe). From ViaCrypt, in Phoenix (602-944-0773).

· RIPEM, shareware similar to ViaCrypt PGP but more rudimentary: it encrypts text files only and can process only files of 48 kilobytes or less. For DOS, Windows, or Macintosh. Available free from RSA, in Redwood Shores, Calif. (415-595-8782). The program can be downloaded on-line via RSARESRSA.COM. -- Researched by Phaedra Hise

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