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                       MDC SOFTWARE, INC.
            Is Proud to Announce the Integrity Shell:
               A New Breed Of Antiviral Software.

        The Integrity Shell is an MSDOS command interpreter or
"shell" which provides more protection for its price than any
other antiviral software. The shell is a natural, user-friendly
environment which allows easy program development, yet provides
an high degree of protection against computer viruses. All types
of programs are protected (Batch files, COM and EXE files). In
addition, protection is provided for programs that have never
been run before (possible viruses or Trojan horses).

        The integrity shell dynamically maintains a list of all
programs which are run. Modified, (possibly infected) or new
programs (possible Trojan horses) are not run without
confirmation. A high-speed cryptographic checksum verifies
program integrity in a minimum amount of time. This checksum
requires about the same amount of time as a highly optimized non-
secure checksum or CRC, but is extremely difficult for a virus
writer to "break" or forge.

        Operation and installation is simple. The shell is started
from the DOS prompt, or from the 'AUTOEXEC.BAT' file. The program
presents the MSDOS environment, with transparent checking
embedded before program execution. No time penalty is paid during
program execution. A supplied program creates a master list of
the most frequently run programs, or the list can be built by the
shell one program at a time. If a program has changed since it
was last run, a query is given. For program development, simply
answer 'y' to the prompt, and the new program information is
saved (and the user is assured not re-testing an old version of a
program).  Answering 'n' to the prompt will cause the program to
not be run.  If no programs change and no new programs are run,
operation of the shell is transparent aside from a slight delay
in loading of programs due to the checking. The delay is
approximately 1 second for an average program (17.5 Kilobytes).

        The main distinctions between this software and other
antiviral software are:

        - The use of a cryptographic checksum.

        - The fact that it is a command interpreter, not a memory-
                resident (TSR) program.

        - The existence of a solid mathematical model of the
                protection.

        - Checking of the boot sector.

        - Checking COMMAND.COM before execution.

        - A unique self-test feature.
        It has been proven mathematically that this software
protects against a large class of computer viruses and Trojan
horses (Matt Cohen, "A New Integrity-Based Model For Limited
Protection Against Computer Viruses", Master's Thesis, The
Pennsylvania State University, 1988).



The package includes the following programs:

                AVSH - The Integrity Shell.

          VIRUSCK - A screening program.

         CHECKALL - A program to check all protected programs. This
                          program replaces a startup-checking system.

      ADDFILES - A program to add files to the protected list.


                          PRICE: 29.95


                        MDC SOFTWARE Inc.
                      Post Office Box 10589
                  State College, PA 16805-0589