Encyclopedia entry
Updated:
Apr 16, 2012
| Published:
Mar 02, 2007
Aliases
TR/Dldr.DNSChanger
(Avira)
-
Win32/Alureon
(CA)
-
Trojan.DnsChange
(Dr.Web)
-
Trojan.Zlob
(Ikarus)
-
Trojan-Downloader.Win32.Zlob
(Kaspersky)
-
DNSChanger
(McAfee)
-
Troj/Zlob
(Sophos)
-
Trojan-Downloader.Win32.Femad
(Sunbelt Software)
-
Trojan.Zlob
(Symantec)
-
TROJ_DNSCHAN
(Trend Micro)
Alert Level
(?)
High
Antimalware protection details
Microsoft recommends that you download the
latest definitions
to get protected.
Summary
Win32/Alureon is a family of data-stealing trojans. These trojans allow an attacker to intercept incoming and outgoing Internet traffic in order to gather confidential information such as user names, passwords, and credit card data. It may also allow an attacker to transmit malicious data to the infected computer. The trojan may modify DNS settings on the host computer to enable the attacker to perform these tasks. Therefore it may be necessary to reconfigure DNS settings after the trojan is removed from the computer.
Win32/Alureon may also infect and corrupt certain driver files, causing them to become unusable.
Symptoms
Symptoms of a Win32/Alureon infection may vary according to the particular variant, for example:
Technical Information (Analysis)
Win32/Alureon is a family of data-stealing trojans. These trojans allow an attacker to intercept incoming and outgoing Internet traffic in order to gather confidential information such as user names, passwords, and credit card data. It may also allow an attacker to transmit malicious data to the infected computer. The trojan may modify DNS settings on the host computer to enable the attacker to perform these tasks. As a result, it may be necessary to reconfigure DNS settings after disinfection.
Instances of the Win32/Alureon trojan may contain various malicious components. The following are three examples of these components:
One component of the Win32/Alureon family specifies the DNS servers to be used by the host computer. To do so, this component sets DNS server addresses for each network adapter on the host computer by modifying values in certain registry subkeys associated with the adapters. For example, the trojan component may:
- Modify registry value: "DhcpNameServer"
under subkey: HKLM\System\CurrentControlSet\Services\Tcpip\Parameters
- Modify registry values:
"NameServer"
"DhcpNameServer"
under certain subkeys of the subkey:
HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces
The same component may also set the fields "IpDnsAddress" and "IpDns2Address" to specific DNS servers in the Windows dial-up configuration file that is for the All Users profile. The trojan sets these fields if the configuration file already contains data. The dial-up configuration file location for the All Users Profile for Windows XP,Server 2003, and Vista is:
- %allusersprofile%\Application Data\Microsoft\Network\Connections\Pbk\rasphone.pbk
To allow these new DNS settings to take immediate effect, the Win32/Alureon trojan runs the following commands:
ipconfig.exe /flushdns
ipconfig.exe /registerdns
ipconfig.exe /dnsflush
ipconfig.exe /renew
ipconfig.exe /renew_all
A second Win32/Alureon component may perform the following operations:
-
Create a randomly named copy of itself under the Windows system folder.
Note - <system folder> refers to a variable location that is determined by the malware by querying the Operating System. The default installation location for the System folder for Windows 2000 and NT is C:\Winnt\System32; and for XP, Vista, and 7 is C:\Windows\System32.
-
Inject threads into local processes to delete itself and perform other tasks.
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Create registry entries under the key HKCR.
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Create registry subkeys such as: HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\ruins
A third Win32/Alureon component may perform the following operations:
-
Gather URLs from the user's Web-browsing history.
-
Create a new registry value in subkey
HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion
and place random data in that value.
-
Create a randomly named copy of itself under the Windows system folder
-
Modify the registry to cause the trojan copy to run automatically each time Windows starts:
Adds value: <name of trojan copy>
With data: <path to trojan copy>
In subkey: HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
-
Delete the following registry entries under subkey HKLM\Software\Microsoft\Windows\CurrentVersion\Run:
-
Run Internet Explorer or the default Web browser and inject code into the corresponding new process. The injected code may take various actions, including changing DNS server settings on the host computer and downloading and running files from certain Web sites.
-
Run a new instance of explorer.exe and inject code into the corresponding new process. The injected code may take various actions, including deleting the trojan file that is running.
Recent variants of Win32/Alureon may be capable of infecting the miniport driver associated with the hard disk of the operating system, causing the driver file to become corrupted and unusable. For the most common system configuration, that is, for computers using ATA hard disk drives, the ATA miniport driver "atapi.sys" is the target driver file. However, other files may also be targeted.
The top ten most commonly-targeted driver files are the following:
atapi.sys
iastor.sys
iastorv.sys
idechndr.sys
nvata.sys
nvatabus.sys
nvgts.sys
nvstor.sys
nvstor32.sys
sisraid.sys
Some Win32/Alureon components may disable or clear the existing Internet Explorer proxy settings.
Prevention
Take the following steps to help prevent infection on your computer:
-
Enable a firewall on your computer.
-
Get the latest computer updates for all your installed software.
-
Use up-to-date antivirus software.
-
Limit user privileges on the computer.
-
Use caution when opening attachments and accepting file transfers.
-
Use caution when clicking on links to web pages.
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Avoid downloading pirated software.
-
Protect yourself against social engineering attacks.
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Use strong passwords.
Enable a firewall on your computer
Use a third-party firewall product or turn on the Microsoft Windows Internet Connection Firewall.
Get the latest computer updates
Updates help protect your computer from viruses, worms, and other threats as they are discovered. It is important to install updates for all the software that is installed in your computer. These are usually available from vendor websites.
You can use the Automatic Updates feature in Windows to automatically download future Microsoft security updates while your computer is on and connected to the Internet.
Use up-to-date antivirus software
Limit user privileges on the computer
Starting with Windows Vista and Windows 7, Microsoft introduced User Account Control (UAC), which, when enabled, allowed users to run with least user privileges. This scenario limits the possibility of attacks by malware and other threats that require administrative privileges to run.
You can configure UAC in your computer to meet your preferences:
Use caution when opening attachments and accepting file transfers
Exercise caution with email and attachments received from unknown sources, or received unexpectedly from known sources. Use extreme caution when accepting file transfers from known or unknown sources.
Use caution when clicking on links to web pages
Exercise caution with links to web pages that you receive from unknown sources, especially if the links are to a webpage that you are not familiar with, unsure of the destination of, or suspicious of. Malicious software may be installed in your computer simply by visiting a webpage with harmful content.
Avoid downloading pirated software
Threats may also be bundled with software and files that are available for download on various torrent sites. Downloading "cracked" or "pirated" software from these sites carries not only the risk of being infected with malware, but is also illegal. For more information, see '
The risks of obtaining and using pirated software'.
Protect yourself from social engineering attacks
While attackers may attempt to exploit vulnerabilities in hardware or software to compromise a computer, they also attempt to exploit vulnerabilities in human behavior to do the same. When an attacker attempts to take advantage of human behavior to persuade the affected user to perform an action of the attacker's choice, it is known as 'social engineering'. Essentially, social engineering is an attack against the human interface of the targeted computer. For more information, see '
What is social engineering?'.
Use strong passwords
Attackers may try to gain access to your Windows account by guessing your password. It is therefore important that you use a strong password – one that cannot be easily guessed by an attacker. A strong password is one that has at least eight characters, and combines letters, numbers, and symbols. For more information, see
http://www.microsoft.com/protect/yourself/password/create.mspx.
Recovery
The Win32/Alureon trojan may enable an attacker to transmit malicious data to the infected computer. Recovering from this situation may require measures beyond removing the trojan itself from the computer.
To detect and remove this threat and other malicious software that may be installed in your computer, run a full-system scan with an up-to-date antivirus product such as the following:
Additional recovery instructions
This threat uses stealth, and you may need to boot to a trusted environment in order to remove it. The threat may also make changes to your computer that makes it difficult for you to download, install or update your virus protection, whether you have a complete antivirus such as
Microsoft Security Essentials installed on your computer or not.
If you suspect your computer has been compromised, we recommend using the Windows Defender Offline to detect and remove this threat.
Using Windows Defender Offline
The way Windows Defender Offline works, is by allowing you to:
- Download a copy of the tool from a computer that has access to the internet
- Save a copy of the recovery tool to a removable drive, in order to create bootable media
- Run the recovery tool on a compromised computer
You might want to use Windows Defender Offline when:
- You need to scan your computer to check for rootkits and other malware
- You are infected with malware that prevents you from downloading and installing an antivirus or the latest updates for your antivirus software
- Your antivirus does not detect or remove advanced malware, such as a rootkit
Note: Windows Defender Offline is not a replacement for a full antivirus solution providing ongoing protection; it is meant to be used in situations where you cannot start or otherwise effectively scan your infected computer due to a virus or other malware actively running on the computer and impeding the effective action of antimalware software. For no-cost, real-time protection that helps guard your home or small business computers against viruses, spyware, and other malicious software, download Microsoft Security Essentials.
- Determine if you require the 32-bit or 64-bit download.
See the Microsoft Help and Support article for instructions on how to determine whether a computer is running a 32-bit version or 64-bit architecture of the Windows operating system.
- Using a computer that can connect to the internet, download the version of the Windows Defender Offline that applies to the affected computer.
If the affected computer is a:
- 32-bit computer, then download the 32-bit version here.
- 64-bit computer, then download the 64-bit version here.
Note: In order for the recovery tool to be effective, make sure you download the version that matches the architecture of the affected computer. For example, if your 64-bit desktop is affected, you will need to download the 64-bit version of the Windows Defender Offline and save it to a removable drive.
- Save the downloaded file to a local drive on your computer.
- Launch the downloaded file, and create a bootable device by following the instructions on the wizard.
Note: We recommend creating a bootable USB or CD; if you create a bootable USB, this can be updated for future use.
- From the affected computer, boot from the USB or CD you created in step 4.
Note: You may need to set the boot order in the BIOS to do this. This will be device specific, so if you are unsure, refer to your system manual or manufacturer.
- Follow the prompts to run a full system scan.
Depending on the outcome of the scan, your next steps will vary. Follow the prompts from Windows Defender Offline to manage any threat detections.
Steps you can take once your computer has been cleaned
- Install security software, such as Microsoft Security Essentials, or any number of other products that provide a complete, real-time antivirus solution.
- Keep your antivirus up to date by making sure you have the latest definitions.
- Use the Microsoft Safety Scanner if you suspect you are infected but are unable to confirm this with your existing antivirus solution.
Restoring Corrupted Files
In some instances, Alureon may modify certain driver files such that they become corrupted and unusable. These corrupted files that will NOT be restored by detecting and removing this threat. In order to restore functionality to the computer, the corrupted file must be restored from backup. Users are advised to boot into a recovery environment and manually replace the file with a clean copy.
Restoring DNS Settings
The Domain Name System (DNS) is used (among other things) to map domain names to IP addresses - that is, to map human-readable domain names to machine-readable IP addresses. When a user attempts to visit a particular URL, a browser will use DNS servers to find the correct IP address of the requested domain. When a user is directed to a malicious server that is not part of the authoritative Domain Name System, an attacker can provide incorrect IP addresses at their choice to map to particular domain names, thus directing the user to possibly bogus or malicious sites without the affected user's knowledge.
Win32/Alureon may modify DNS settings on the host computer, thus the following steps may be required after the removal is complete:
-
If the computer has a network interface that does not receive a configuration using DHCP, reset the DNS configuration if necessary. For information on configuring TCP/IP to use DNS in Windows XP, see
http://support.microsoft.com/kb/305553
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If a dial-up connection is sometimes used from the computer, reconfigure the dial-up settings in the rasphone.pbk file as necessary, as the trojan may set the fields "IpDnsAddress" and "IpDns2Address" in the rasphone.pbk file to the attacker's address. The Microsoft scanner code that automatically removes the trojan backs up the infected dial-up configuration file to:
%ALLUSERSPROFILE%\Application Data\Microsoft\Network\Connections\Pbk\rasphone.pbk.bak
