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10.3 Technical Malware Attack Methods: From Viruses to Denial of Service 305

Figure 10.4 How a computer
virus can spread

Worms code. Users are tricked into executing an infected file, where it
attacks the host, anywhere from inserting pop-up windows to
Unlike a virus, a worm can replicate itself automatically (as a damaging the host by deleting files, spreading malware, and so
“standalone”—without any host or human activation). Worms forth. The name is derived from the Trojan horse in Greek
use networks to propagate and infect a computer or handheld mythology. Legend has it that during the Trojan War, the city
device and can even spread via instant messages or e-mail. In of Troy was presented with a large wooden horse as a gift to
addition, unlike viruses that generally are confined within a the goddess Athena. The Trojans hauled the horse inside the
target computer, a worm can infect many devices in a network city gates. During the night, Greek soldiers who were hiding in
as well as degrade the network’s performance. According to the hollow horse opened the gates of Troy and let in the Greek
Cisco, “worms either exploit a vulnerability on the target sys- army. The army was able to take the city and win the war.
tem or use some kind of social engineering to trick users into Trojans spread only by user interaction (e.g., such as
executing them.” Because worms spread much more rapidly opening an under the guise of an e-mail allegedly sent by
than viruses, they may be more dangerous. Verizon), and there are many variants of Trojans (e.g., Zeus,
W32).
Macro Viruses and Microworms
A macro virus (macro worm) is a malware code that is Example 1: Trojan-Phisher-Rebery
attached to a data file rather than to an executable program In 2006, a variant of a Trojan horse program named Trojan-
(e.g., a Word file). According to Microsoft, macro viruses can Phisher-Rebery was used to steal tens of thousands of identities
attack Word files as well as any other application that uses a from people in 125 different countries. The Rebery malicious
programming language. When the document is opened or software is an example of a banking Trojan, which is pro-
closed, the virus can spread to other documents on the com- grammed to create damage when users visit certain online
puter’s system. For information about Word macro viruses, see banking or e-commerce sites. For an infographic describing the
Microsoft Support at support.microsoft.com/kb/187243/en. state of financial Trojans see Symantec (2014).
Computer programs that are very similar to viruses are worms
and Trojan horses. Example 2: The DDOS Attacks on WordPress
In March 2014, hackers used a botnet to attack more than
Trojan Horse 162,000 WordPress sites. Given that WordPress powers about
A Trojan horse is a program that seems to be harmless or 17% of the world’s blogging websites, any attack can be
even looks useful but actually contains a hidden malicious devastating.