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amateur malicious code developers are usually just experimenting
with a new tool they downloaded or attempting to cause problems for

one or two enemies. Unfortunately, the malware sometimes spreads
rapidly and creates problems for internet users in general.

In addition, the tools used by script kiddies are freely available to
those with more sinister criminal intent. Indeed, international
organized crime syndicates are known to play a role in malware
proliferation. These criminals, located in countries with weak law

enforcement mechanisms, use malware to steal the money and
identities of people from around the world, especially residents of the
United States. In fact, the Zeus Trojan horse was widely believed to be
the product of an Eastern European organized crime ring seeking to
infect as many systems as possible to log keystrokes and harvest online
banking passwords. Zeus first surfaced in 2007 but continues to be
updated and found in new variants today.

The most recent trend in malware development comes with the rise of
the advanced persistent threat (APT). APTs are sophisticated
adversaries with advanced technical skills and significant financial
resources. These attackers are often military units, intelligence
agencies, or shadowy groups that are likely affiliated with government
agencies. One of the key differences between APT attackers and other
malware authors is that these malware developers often have access to

zero-day exploits that are not known to software vendors. Because the
vendor is not aware of the vulnerability, there is no patch, and the
exploit is highly effective. Malware built by APTs is highly targeted,
designed to impact only a small number of adversary systems (often as
small as one!), and difficult to defeat. You’ll read later in this chapter
about Stuxnet, one example of APT-developed malware.

Viruses

The computer virus is perhaps the earliest form of malicious code to
plague security administrators. Indeed, viruses are so prevalent
nowadays that major outbreaks receive attention from the mass media
and provoke mild hysteria among average computer users. According

to Symantec, one of the major antivirus software vendors, there were
over 357 million strains of malicious code roaming the global network