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The Bad Guys from Outside: Malware

  • Sample Chapter is provided courtesy of Cisco Press.
  • Date: Apr 29, 2010.

Chapter Description

In this chapter, you'll learn how malware works and why it presents such a threat to the enterprise. In addition, you learn about the newest sophisticated tactics that malware creators use to trick computer users into downloading their wares.

This chapter includes the following topics:

  • Modern Malware Overview
  • Finding the Weak Points
  • Social Engineering for Success
  • Spamming and Phishing Get Targeted
  • Profit Motive

Along with acceptable use policies (AUP) and data loss prevention (DLP), malware, or malicious software, is one of the three critical areas that enterprise security policies must address. Malware is pervasive, painful, and expensive to detect and block.

Malware has been part of computing for decades. In the 1990s, it got onto your computer or network when you stuck an infected floppy disk into your drive, or when a clever hacker gained access to your network. Then, with email becoming more prevalent, hackers designed malware to spread as infected email attachments. Today, the Internet is a fantastic distribution mechanism for malware.

In this chapter, you can find out how malware works and why it presents such a threat to the enterprise. In addition, you learn about the newest sophisticated tactics that malware creators use to trick computer users into downloading their wares.

Modern Malware Overview

Malware, which is malicious software that infiltrates computers, networks, and mobile devices, is part of life in the information age. Malware is sent via email, spreads via portable media storage and drives—such as CDs, USB drives, and MP3 players—and can secretly download onto your computer from websites you trust.

Today, the primary distribution mechanism for malware is the World Wide Web. Malware is served not only from entirely malicious, fraudulent websites but also legitimate websites that have been compromised.

One way in which malware has changed over time is that it's a lot smarter and harder to detect than before. This makes it very difficult to get it out of your systems after they are infected. But malware still depends on vulnerabilities in technology—and weaknesses in human nature—to infiltrate computers and networks.

And hackers aren't trying to get malware onto your computers just for fun, or to see how far they can spread the code they wrote. Modern malware is a for-profit, big-business undertaking. Online criminals invest significant amounts of money and time in more efficient malware and better malware distribution mechanisms because they know the financial rewards can be enormous.

Types of Malware

The original email–propagated viruses, such as the circa-2000 Melissa or I Love You viruses, did not do much besides slow down the performance of your computer and your network. They soaked up bandwidth and processing power by sending copies of themselves to millions of people. This type of malware was created primarily to enable its authors to show off their "development" skills. For David Smith of New Jersey, the author of the Melissa virus, the erstwhile use of his computer skills backfired; following a tip from an AOL employee to law enforcement, Smith ended up spending 20 months in prison.

Following the success of these earlier mass-mailer viruses, a new class of malware was born. This malware, or spyware, was used to deliver pop-up ads. A full spectrum of pop-up ad malware exists, ranging from the legitimate but annoying to the illegitimate and harmful.

A good example of legitimate but annoying spyware is the pop-up ad generators (also called adware) often embedded in peer-to-peer applications, such as Kazaa. Users downloading the desired application had to agree to install the adware, but the adware was virtually impossible to remove. Many other pop-up generators and tracking cookies are loaded onto a user's PC without their knowledge, creating annoying ads and capturing personal web browsing information to help target more unwanted advertising.

Other forms of malware are more hostile. A particularly ugly variant of malware, known as ransomware, shuts down functionality of the end user device unless the victim pays a ransom. In 2008, several kinds of malware and ransomware for mobile phones showed up in Asia, where workers are more likely to have a mobile phone than a personal computer. As VNUnet reported, when the mobile phone was infected, the phone's owner would receive a message instructing them to pay to restore the phone's functionality.1

In a classic scam, a lot of computer-based ransomware masquerades as antispyware or antivirus software. It pretends to scan your computer for malware, tells you your device is infected, and asks you to fork over money to access the "full" version of the software that can remove the "found" infections. In 2008, a family of fake antivirus software, known as XP Antivirus, infected millions of computers netting the criminals millions of dollars.

Keylogging malware tracks every keystroke you make and sends the information back to online criminals so that they can use or resell your login names, passwords, credit card numbers, and other useful personal or corporate information.

Rootkits gain access to the core of your operating system and let criminals control your computer or network as administrators. (Some of the fake antimalware products partake in these activities instead of, or as well as, demanding money to "clean" your computer.) After criminals infiltrate your computer, they want to use it to profit. To do so, they make it part of a botnet, which is a network of thousands of infected computers that carry out the orders of online criminals by sending out massive amounts of spam, hosting websites, or participating in attacks on websites that are designed to deny visitors access to the sites (also known as a denial of service attack). This type of malware can also turn these websites into malware redirect hubs.

Another technique used by criminals is to create malicious software that looks for a flaw in the browser code or, more often, a flaw in a browser plug-in such as the Flash player. The malware creates a buffer overflow. This is one of the most common and dangerous vulnerabilities; malware piles extra data into a program's buffer or temporary data storage area. Rather than rejecting the extra data, the vulnerable software enables the extra data to be written to the next operation. A carefully crafted exploit can ensure the extra data is an attack vector, which is written to an overflow area that executes the attack. The most common exploits today target web browsers or browser plug-ins such as the Flash player or Adobe Reader. In this case, the victims merely visit a website and can be exploited and have malware installed on their computer without their interaction or knowledge; this is known as a drive-by download.

A 2008 Google study of drive-by downloads indicated that more than 3 million URLs on the Internet were found to initiate drive-by downloads. And 1.3 percent of incoming search queries to Google brought up at least one malicious URL in the search results.2


Botnets are the backbone of criminal activity on the Internet today, and they keep growing in number and sophistication. Internet experts have likened botnets to a pandemic, and say that at one time, up to 25 percent of all Internet-connected computers were part of a botnet.3 With the steady rollout of broadband infrastructure and unprotected PCs in the emerging economies of the world, the supply of botnets appears unlimited.

Usually, the computer owner won't even know the computer is part of a botnet except for occasional slowdowns in performance. The malware that turns the computer into a botnet node, or "zombie," often invisibly downloads in the background while the computer user innocently surfs the Web. It can also be very clever at hiding from antivirus software, with code that changes every so often (making it harder to identify) or goes dormant for a while (making it harder to find).

Even Trusted Sites Can't Be Trusted

A recent development in malware distribution is the infection of legitimate websites—in enormous numbers—so they start serving up malware. The advantage for malware creators: These sites have been around for a long time, have a good reputation, and are trusted by large numbers of site visitors and security solutions—so they might be easier to exploit.

Modern malware has managed to penetrate the websites of media organizations and publications such as BusinessWeek,4 major companies, government organizations, banks, and online social networks. This enables criminals to take advantage of the millions of visitors to these trusted sites without having the inconvenience and expense of building appealing malware-distributing websites of their own.

In these cases, online criminals attack millions of legitimate websites looking for weaknesses. If they find a vulnerable site, they insert small bits of code, called iFrames, on these trusted webpages so that they start sending visitors to websites that host malware. The iFrame codes make it possible to embed one HTML document inside another one. For instance, the banner ad found on a webpage is often hosted by a different web server than the main content. Online criminals can simply incorporate a malicious URL somewhere in the iFrame, or they can hide it with JavaScript.

How do online criminals get their malicious iFrame onto a legitimate website? Most often, they use SQL injections.

This technique exploits a vulnerability in the database layer of certain web applications and servers. When website developers don't properly sanitize the data transmitted in user input fields (such as forms and user logins) on webpages that use SQL, criminals can take advantage of this weakness to take control of the website and turn it into a malware redirection hub.

2. Finding the Weak Points | Next Section

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