Surveillance or Security?: The Risks Posed by New Wiretapping Technologies by Susan Landau

forms of attack.
    3.5 Attacks on the Hosts
    End hosts face attacks from three types of malicious software, or malware:
    • Worms, which are self-replicating programs that spread throughout a
machine or between machines.
    • Viruses, which are self-replicating program fragments (rather than complete programs); these must be inserted into a program in order to work.

    • Trojan horses, which are programs that hide some malicious behavior
within an attractive functionality; the attractive aspect often tempts the
user to download the program. Trojan horses can be used to deliver viruses
or worms.
    Such malware can enter a user's machine in various ways. It may arrive
unbidden via the Internet, as the Morris worm did, or via removable media
such as a floppy disk, which is how the first such virus spread in 1982.63
It may be downloaded as an attachment in an email and then opened;
that is how both the 1999 Melissa and the 2000 ILOVEYOU viruses64
arrived on users' machines.
    Commonly users are attacked only by Trojan-horse programs that they
have explicitly downloaded to their machine (typically the user downloads
the program because of some attractive functionality; the user is unaware
of the other functionality-such as random shutdowns, or redirecting the
browser to a pornography site-that might occur once the Trojan horse is
installed). But users can also be threatened by a more insidious form of
Trojan-horse attack, referred to as "drive-by download," which arrives when
the user visits an infected web page. Small pieces of code can be embedded
within the code of vulnerable websites. This code then invisibly and automatically installs malware on any vulnerable machine whose user visits
the infected site. The malware gains control over the compromised system,
perhaps stealing sensitive information (e.g., banking passwords when the
user is visiting a banking website), perhaps sending out spam, and so forth.65
    Different sets of vulnerabilities are exploited in this type of attack: the
website has vulnerabilities allowing malware to be installed in its html
code, and this malware installs other software on a vulnerable network
host. Such a dual-level attack reflects a different level of sophistication than
previous attacks on user machines.
    One might ask how users' machines came to be so vulnerable to subversion. The answer starts with the fact that decades ago when personal
computers were first designed, they were standalone machines. The model
was that the user should have full access to all functions on the machine.
This has distinct advantages; in particular, it allows the user to do anything
she wants on the machine. But such a model becomes problematic when
the machine is networked. If the user can do anything she wants on her
machine, then if her computer is not properly secured, anyone else having
access to her machine can also do anything they want to it. Add to this
situation the fact that securing computers is not easy. Computer operating
systems are highly complex systems. It is very difficult to completely eliminate mistakes in the millions of lines of code in them, but it is possible to do better than present systems. NASA's shuttle software, for example, has
a rather remarkable record."

    The business model for high tech conspires against security. Being first
to market is extremely important, and security concerns have often been
relegated to a backwater to be fixed in "version 2.0." Often version 2.0
never comes. In any case, by the time it does, it is often too late-too many
machines with poor security paradigms have already been purchased and
deployed.
    One might imagine that somewhere on the network it would be possible
to examine packets before they arrive at a vulnerable machine and thus
stop attacks before they start. Firewalls are a step in this direction. A firewall
is a device interposed between an internal network (e.g., home, university,
corporate, etc.) and