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8.7. Data Stealers: Making Money with Viruses

Modern attackers are making money using computer viruses. Although professional attackers could make money by breaking into individual systems to steal credit card numbers and other valuable information, computer worm attacks can reach many more targets in much less time, thereby enhancing the chances that the attacker gets away with valuable information without a trace.

8.7.1. Phishing Attacks

There are several ways to use computer worms to steal information. In the simplest cases, the attacker uses a social engineering attack (also called a simple phishing attack) to collect the information simply by asking you to disclose your credit card information and PIN number. Phishing attacks typically use spoofed e-mail and fraudulent Web sites designed to fool recipients to disclose personal information. Phishers are able to convince up to 5% of recipients to respond to them10.

The W32/Mimail.I@mm11 is an example of such a simple, but rather effective attack. The worms sends itself in e-mail messages. In its attempt to steal information, the worm displays fake dialogs purporting to be from PayPal (see Figure 8.8), which ask you to type in a credit card number and other personal information. The stolen information is stored. Then the information is subsequently encrypted and sent to the attacker.

Figure 8.8. The dialog box displayed by the W32/Mimail.I@mm worm.


8.7.2. Backdoor Features

Computer worms often have built-in backdoors. An infamous example of such a worm is W32/HLLW.Qaz.A. This worm was first discovered in China in July of 2000. QAZ is a companion virus, but it also spreads itself over the network. Furthermore, the worm has a backdoor that will enable a remote user to connect to and control the computer using port 7597.

QAZ enumerates through poorly protected NetBIOS shares and attempts to find a computer to infect. After the remote computer is infected, its IP address is e-mailed back to the attacker. The backdoor payload in the virus awaits connection. This enables a hacker to connect and gain access to the infected computer. According to several sources, QAZ was most likely responsible for successful attacks against Microsoft's networks, compromising a nonsecured home system that had remote connections to corporate sites, thereby allowing the attacker access to valuable information.

Another famous backdoor incident was built into a variant of CodeRed, called CodeRed_II. This worm copies CMD.EXE from the Windows NT \System folder to the following folders (if they exist):

C:\Inetpub\Scripts\Root.exe

D:\Inetpub\Scripts\Root.exe

C:\Progra~1\Common~1\System\MSADC\Root.exe

D:\Progra~1\Common~1\System\MSADC\Root.exe

Although CodeRed_II spreads as an in-memory injector just like the original, this variant of the worm also drops a Trojan called VirtualRoot. When executed, this Trojan modifies the following Registry key:

HKLM\System\CurrentControlSet\Services\W3SVC\Parameters\Virtual Roots

The Trojan adds a few new keys here and sets the user group on these to the value 217. This allows the intruder to control the Web server by sending an HTTP GET request to run scripts/root.exe on the infected Web server. After a successful attack, you can find new root accesses to C:\ and D:\ drives in the Computer Management feature of Windows, as shown in Figure 8.9. This allows the attacker full remote access to logical drives C: and D: on the infected computer through legitimate requests to the Web server.

Figure 8.9. System with opened shares after a CodRed_II attack.


Computer viruses used backdoor features targeting Novell NetWare servers as well. For example, the Hypervisor virus12 on DOS included a special payload to create a Supervisor-equivalent user, called Hypervisor, on Novell NetWare servers in 1995.

Hypervisor waits patiently until the Supervisor of the network logs on from an infected system. At that moment, the virus will be able to add a new user, creating a Hypervisor user object and adding SUPERVISOR SECURITY_EQUALS attributes to it. The Hypervisor user will not have a password set; thus the attacker can log in to the system with Supervisor rights shortly after the virus has been introduced on the local network. Hypervisor also copies the bindery files of Novell NetWare to the SYS:LOGIN/ folder (NET$BIND.SYS, NET$BVAL.SYS on 2.xx servers and NET$OBJ.SYS, NET$PROP.SYS on 3.xx servers). In addition, Hypervisor is a stealth virus.

Computer worms such as Nimda use a similar approach on Windows systems. Nimda adds the Guest account to the Administrator group. This gives the Guest account administrative privileges.

Another example is the W32/Bugbear@mm family, which spreads using a variety of techniques including mass-mailing, network share infection, and file infection. In addition, Bugbear variants support a backdoor component and a keylogger function. Using the keylogger, the worm can collect information that the user types on the system, which can include sensitive data. The worm sends the collected information to several e-mail accounts that belong to the attacker. Using the backdoor component, the attacker can connect to the compromised systems remotely. In addition, some variants of Bugbear specifically target financial institutions. The worm carries a long list of more than 1,000 domain names that belong to banks from around the world. When Bugbear determines that the default e-mail address of the local system belongs to a banking company, it will send the data collected by the keylogger, as well as cached dial-up password information to the e-mail accounts of the attacker. Using the information, the attacker hopes to connect to a financial institution's dial-up network and make financial gain.

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