In the often repeated story of the Trojan horse used to get
inside and attack the fortified and well-defended city of Troy
from within, invaders used something that was seemingly
benign as a vehicle for the attack: a large wooden horse.
Similarly, Trojan horses of the information security world
are seemingly benign programs that attack computer
systems from within.
Once inside the computer, a Trojan program commonly
replaces key system files and/or programs with malicious
versions of the same. When these programs are executed,
they perform their predetermined destructive activities,
and users are powerless to stop them.
For example, an attacker may replace one of the Windows
operating system dynamically linked libraries (DLLs) with
a malicious version. DLLs are program files that Windows
calls on to perform various tasks. An attacker may replace
one of these DLLs with a Trojan horse version that does
everything the normal DLL did, and a little more. That little
more may be any number of things, from reformatting the
hard drive to stealing credit card numbers.
In recent months, spyware and potentially unwanted
programs have begun to wreak more havoc than worms
or viruses. Although often unseen at first, PC users,
particularly users connecting to the Internet from home,
have increasingly noticed that their PCs are becoming
slower and programs are crashing more often. In many
cases, their PCs have become almost useless, because the
memory and the processing power of the machines is taken
up trying to send their private information from their PCs to
the Internet. Or they are fighting off a myriad of unwanted
spam advertisements that pop up onto their computer
screens and advertise goods from all over the world. Most
annoying of all, is the advertisement that continuously
announces to and reminds the frustrated user that their PC
now has a potentially unwanted program and they should
purchase a particular software solution to clean it up.
Recently, hackers have utilized the distributed resources
of thousands of Internet-connected PCs to launch
Denial of Service (DoS) attacks against unlucky targeted
organizations or servers. This is done by the master hackers
who deposit their software code by Trojan horse onto the
PCs, which then register with their host and await further
instructions as to when and how to launch an attack. At
a time chosen by the master hacker, the PC robots (bots),
under external control, will launch their code and attack the
designated target from the unwitting residential owner’s
PC. This way, the master attacker remains anonymous,
but thanks to the unprotected home user, can utilize the
resources of thousands of computers around the world to
achieve his goal.
