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VIRSTOP

The primary purpose of the VIRSTOP.EXE program is to prevent the execution
of programs infected with known viruses.

VIRSTOP installs itself in RAM as a standard TSR and intercepts the
so-called "Load-and-execute" function. This means that whenever an attempt
is made to run a program VIRSTOP gets a chance to examine it first.

VIRSTOP uses a simple but fast search to check for viruses, but it does
not make an accurate identification - F-PROT.EXE is necessary for that
purpose.

IMPORTANT! ... VIRSTOP does not detect the same number of viruses as
F-PROT. In particular, VIRSTOP does not detect most polymorphic viruses.
It is therefore recommended that VIRSTOP only be used as one component of
the virus protection - do not rely on it alone.

If VIRSTOP finds a virus, it will abort the execution of the program,
display a message and return an error. For example, if you attempt to run
a program infected with the Cascade virus, with VIRSTOP active in memory,
you might see something like this:

This program is infected with the Cascade virus.
Cannot execute A:\INF-PROG.COM

VIRSTOP has a secondary function as well - it attempts to check for any
active boot sector virus when it is run.

The recommended way to load VIRSTOP is to load it from the CONFIG.SYS
file, with a command such as:

DEVICE=C:\F-PROT\VIRSTOP.EXE

Or, if you are using DOS 5 (or 6), you can instead use

DEVICEHIGH=C:\F-PROT\VIRSTOP.EXE

IMPORTANT! - If any memory managers, such ar 386MAX, HIMEM or QEMM are
used, they must be loaded before VIRSTOP.

In order to test if VIRSTOP is properly installed, the program F-TEST is
provided. It is NOT a virus, but it is detected by VIRSTOP the same way as
a virus-infected program.

If VIRSTOP is not installed or not active, F-TEST will print out a message
saying so when run and return a code of 1, which can be checked with the
ERRORLEVEL command. If VIRSTOP is active and working, it will display a
message to that effect.

If you are using software that takes over the "load-and-execute" function,
in particular Novell Netware and PC-NFS, F-TEST may say that VIRSTOP is
not active. To make VIRSTOP work properly under those circumstances, you
must either...

Load VIRSTOP from AUTOEXEC.BAT (after the network software is loaded),
instead of CONFIG.SYS.

or

Put a command like the following in AUTOEXEC.BAT, after you load
the network software:

C:\F-PROT\VIRSTOP /REHOOK

VIRSTOP.EXE includes one additional feature - it is designed to be able to
detect if it has been infected by a "stealth" virus. It is also often (but
not always) able to detect attempts to run "stealth"-virus infected
programs, even though the virus is active in memory.

VIRSTOP supports the following command-line switches:

/DISK:X - do not store search strings in memory, but read them
in from disk when necessary. This reduces the memory requirements
down to around 3500 bytes. The :X indicates which drive to use for
store the two "swap" files, _VIRSTOP.TMP (which stores the part
of memory overwritten by VIRSTOP) and _VIRSTOP.SWP, which is a
copy of VIRSTOP.EXE, allowing the original copy to be updated
while VIRSTOP is running.

Notes:
If the drive letter is not specified, it defaults to C:

The drive should be a fast, local drive - not a network
drive. RAMdisks are ideal.

/DISK can now be used if you run VIRSTOP from a diskette
which is later removed, as the original file is not
accessed, just the _VIRSTOP.SWP copy.

If this switch is used, and VIRSTOP is loaded from CONFIG.SYS,
it is critical that the full path name is given.

DO NOT USE /DISK IF YOU USE DEVICEHIGH= TO LOAD VIRSTOP
(LOADHI seems to work OK, though).

/OLD - do not complain, even if the program has "expired". Use of
this switch is not recommended.

/REHOOK Re-hook INT 21h, if VIRSTOP was loaded before Netware or
another similar program that takes over the "load-and-execute"
function.

/NOTRACE Using this swith makes VIRSTOP work properly on machines
that are using old (and not 100% Intel-compatible) versions of the
Cyrix 486SLC processor. It will also fix some compatibility
problems with the 386MAX and BlueMax memory managers. However,
this switch should not be used unless necessary, as it makes
VIRSTOP ineffective against stealth viruses that are run before
VIRSTOP is loaded.

/NOMEM Do not perform a memory scan when starting.

/FREEZE Stop the computer when a virus is found.

/[NO]COPY [Do not] check files when they are accessed/copied.
The default is /NOCOPY

/[NO]BOOT [Do not] check boot sectors when a diskette is accessed.
The default is /BOOT.

/[NO]WARM [Do not] check the diskette in drive A: when the user
presses Ctrl-Alt-Del. The default is /NOWARM