A Brief History of Cybercrime and Cyberwarfare - The Technical and Social History of Software Engineering - page 413

it could not just shut them down because all of the infected computers would prob-
ably have stopped working. The FBI could only replace the rogue addresses with
authentic addresses.
The FBI then got a court order that allowed it to keep the host computers run-
ning until July 9, 2012. The reason was to allow time for antivirus companies
and the government to provide tools and methods for safely removing the DNS
Changer without doing serious harm to half a million computers. If the host DNS
Changer computers were merely stopped, then the infected computers would no
longer be able to access the internet.
Tools were made available to check for infections in home and corporate com-
puters, and then other tools were available to remove the Trojan. I used the DNS
analysis tool on all computers used by my family, and fortunately none were in-
fected. The URL of the inspection site was www.dns.ok.us . This site returned a
green image for clean computers and a red image for infected computers. Users of
infected computers were then routed to several repair tools.
A study of the DNS Changer Trojan on the web stated that about 12% of For-
tune 500 companies and 4% of U.S. government computers were infected. No
doubt an even higher percentage of private computers were infected.
The DNS Changer story is a cautionary tale that we should all take seriously.
In the modern world, criminals have the technical ability to attack and seize even
computers that have some protections such as firewalls and antivirus packages.
The fact that a few clever cybercriminals could infect four million computers with
a Trojan is not a good sign for the future when hostile governments might attempt
something similar or worse.
Viruses
A natural virus is a small organism that has the ability to enter cells and divert
RNA into making new copies of the invading virus. A computer virus is a piece of
software that has the ability to invade computers and divert part of its functionality
into making and distributing new copies of the virus and perhaps doing something
harmful as well.
Viruses are harmful for the same reason that cancer is harmful: It metastasizes
and infects and eventually shuts down host organisms. Computer viruses can do
the same thing to operating systems and other kinds of software. The critical fea-
ture of a computer virus is that it can replicate itself and make other copies, which
can then spread to other computers.