Re: checking for all known viruses vs. fixing the system

From: Valdis Kletnieks (valdis.kletnieks@vt.edu)
Date: 02/12/02

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    From: Valdis Kletnieks <valdis.kletnieks@vt.edu>
Date: 12 Feb 2002 10:17:28 -0500

    Dan Jacobson <jidanni@deadspam.com> writes:

    > Um, I'd just like to double check: the idea of a virus scanner program
    > is to scan for all the known viruses that can affect the system. This
    > is due to it being inconvenient to fix the system so it cannot be
    > affected by the viruses. If the system was fixed so that it would
    > not be affected by viruses, it would also become not very useful due
    > to all its functionality being hampered... is this c

    Correct.

    Incidentally, it's a proven fact that you *cannot* write a perfect virus
    checker program - because it's basically the same problem as the
    Turing Halting Problem. Fred Cohen proved that in his paper that
    originally presented the *concept* of computer viruses:

    http://www.all.net/books/virus/index.html

    Also, you might want to read Ken Thompson's classic Turing Award lecture:

    http://www.acm.org/classics/sep95/

    It's not directly about viruses - but everybody needs to be reminded about
    it once in a while anyhow. ;) 

    -- 
				Valdis Kletnieks
				Computer Systems Senior Engineer
				Virginia Tech

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