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just as devastating. Another category of virus writers is the military, which sees vi-
ruses as a weapon of war potentially able to disable an enemy’s computers.
Another issue related to spreading viruses is avoiding detection. Jails have
notoriously bad computing facilities, so Virgil would prefer avoiding them.
ing a virus from his home machine is not a wise idea.
If the attack is successful,
the police might track him down by looking for the virus message with the
youngest timestamp, since that is probably closest to the source of the attack.
To minimize his exposure, Virgil might go to an Internet cafe in a distant city
and log in there.
He can either bring the virus on a USB stick and read it in him-
self, or if the machines do not have USB ports, ask the nice young lady at the desk
to please read in the file
so he can print it. Once it is on his hard disk, he
renames the file
and executes it, infecting the entire LAN with a virus
that triggers a month later, just in case the police decide to ask the airlines for a list
of all people who flew in that week.
An alternative is to forget the USB stick and fetch the virus from a remote Web
or FTP site. Or bring a notebook and plug it in to an Ethernet port that the Internet
cafe has thoughtfully provided for notebook-toting tourists who want to read their
email every day. Once connected to the LAN, Virgil can set out to infect all of the
machines on it.
There is a lot more to be said about viruses.
In particular how they try to hide
and how antivirus software tries to flush them out.
They can even hide inside live
animals—really—see Rieback et al. (2006).
We will come back to these topics
when we get into defenses against malware later in this chapter.
9.9.3 Worms
The first large-scale Internet computer security violation began in the evening
of Nov. 2, 1988, when a Cornell graduate student, Robert Tappan Morris, released
a worm program into the Internet. This action brought down thousands of com-
puters at universities, corporations, and government laboratories all over the world
before it was tracked down and removed. It also started a controversy that has not
yet died down. Wewill discuss the highlights of this event below. For more techni-
cal information see the paper by Spafford et al. (1989).
For the story viewed as a
police thriller, see the book by Hafner and Markoff (1991).
The story began sometime in 1988, when Morris discovered two bugs in
Berkeley UNIX that made it possible to gain unauthorized access to machines all
overthe Internet. As we shall see, one of them was a buffer overflow. Working all
alone, he wrote a self-replicating program, called a
, that would exploit these
errors and replicate itself in seconds on every machine it could gain access to.
worked on the program for months, carefully tuning it and having it try to hide its
It is not known whether the release on Nov. 2, 1988, was intended as a test, or
was the real thing.
In any event, it did bring most of the Sun and VAX systems on

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