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From: mitel!sce!doe.carleton.ca!dfs@uunet.UU.NET (David F. Skoll)
Newsgroups: comp.virus
Subject: Re: Is it possible ? (PC)
Message-ID: <0004.9007121452.AA11310@ubu.cert.sei.cmu.edu>
Date: 11 Jul 90 14:44:13 GMT
Sender: Virus Discussion List <VIRUS-L@LEHIIBM1>
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Approved: krvw@sei.cmu.edu

T.TENG@Macbeth.Stanford.EDU (T. Teng) writes:
>Is it possible to make something for PCs, which works effectively against
>all the virus, old or new?

I wrote a program for the PC called VPROT which "sort of" achieves this.
The program examines files (.EXE, .COM, whatever) and adds a two-byte
checksum to the end of the file.  You can pass the file through an encrypting
filter before generating the checksum to reduce the chances of a virus
realizing the file is protected.

Then, you periodically run the program to ensure that the file checksums
are still valid.  If a virus has modified the file, chances are high that
the checksum is wrong, because I used the CRC-16 generating polynomial.

BUT:

1) This does not protect the boot sector, although the idea can be
   extended to cover this case.

2) If you "protect" files which are ALREADY infected, you're in trouble.

3) You must run the program fairly often to check your files.

4) If a virus is found, you need another tool to disinfect it.

So, is it worth it?  I guess if you copy lots of software from a BBS
or other "suspicious" sources, it is.  Otherwise, I wouldn't bother.

+--------------------------------------------------------------------------+
|  David F. Skoll                     Department of Electronics            |
|  dfs@doe.carleton.ca                Carleton University                  |
|  (613) 788-5771 | 788-5772          Ottawa, Ontario, Canada              |
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