Alert level

TrojanDownloader:Win32/Tracur.A


Encyclopedia entry
Updated: Jun 25, 2009  |  Published: Dec 16, 2008

Aliases
  • Win32/Agent.OAF (ESET)
  • Win32/Vundo.BAW (CA)
  • Trojan-Downloader.Win32.Agent.afky (Kaspersky)

Alert Level (?)
Severe

Antimalware protection details
Microsoft recommends that you download the latest definitions to get protected.
Detection last updated:
Definition: 1.69.995.0
Released: Nov 16, 2009 		Detection initially created:
Definition: 1.47.226.0
Released: Nov 12, 2008

Summary

TrojanDownloader:Win32/Tracur.A is a trojan that downloads and executes arbitrary files.

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Symptoms

There are no obvious symptoms that indicate the presence of this malware on an affected machine.

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Technical Information (Analysis)

TrojanDownloader:Win32/Tracur.A is a trojan that downloads and executes arbitrary files.
Installation
When executed, TrojanDownloader:Win32/Tracur.A drops a file to <system folder>\<random>32.dll, where <random> is a randomly generated string.
 
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 and Vista is C:\Windows\System32.
 
The trojan also modifies the registry to make sure it is loaded into every process at each Windows restart:
 
Adds value: "DllName"
With data: "<system folder>\<dllname>",
To subkey: HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\Notify\<volume>
 
Modifies value: AppInit_Dlls"
With data: "<system folder>\<dllname>",
To subkey: HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Windows.

where <dllname> is the filename of the trojan's DLL, and <volume> is a string derived from the volume serial number.
Payload
Downloads and Executes Arbitrary Files
TrojanDownloader:Win32/Tracur.A listens on an undefined TCP port and waits for instructions. It may be instructed to perform the following actions:
  • Download and execute arbitrary files
  • Redirect the user's web browser to a URL of the attacker's choice, and maximize the web browser Window.
 
Analysis by Chun Feng

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Prevention

Take the following steps to help prevent infection on your system:
  • Enable a firewall on your computer.
  • Get the latest computer updates for all your installed software.
  • Use up-to-date antivirus software.
  • Use caution when opening attachments and accepting file transfers.
  • Use caution when clicking on links to web pages.
  • Protect yourself against social engineering attacks.
Enable a firewall on your computer
Use a third-party firewall product or turn on the Microsoft Windows Internet Connection Firewall.
To turn on the Windows Firewall in Windows Vista
  1. Click Start, and click Control Panel.
  2. Click Security.
  3. Click Turn Windows Firewall on or off.
  4. Select On.
  5. Click OK.
To turn on the Internet Connection Firewall in Windows XP
  1. Click Start, and click Control Panel.
  2. Click Network and Internet Connections. If you do not see Network and Internet Connections, click Switch to Category View.
  3. Click Change Windows Firewall Settings.
  4. Select On.
  5. Click OK.
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.
To turn on Automatic Updates in Windows Vista
  1. Click Start, and click Control Panel. 
  2. Click System and Maintainance.
  3. Click Windows Updates.
  4. Select a setting. Microsoft recommends selecting Install updates automatically and choose a time that is convenient for you. If you do not choose Automatic, but you choose to be notified when updates are ready, a notification balloon appears when new downloads are available to install. Click the notification balloon to review and install the updates.
To turn on Automatic Updates in Windows XP
  1. Click Start, and click Control Panel. 
  2. Click System.
  3. Click Automatic Updates.
  4. Select a setting. Microsoft recommends selecting Automatic. If you do not choose Automatic, but you choose to be notified when updates are ready, a notification balloon appears when new downloads are available to install. Click the notification balloon to review and install the updates.
Use up-to-date antivirus software
Most antivirus software can detect and prevent infection by known malicious software. To help protect you from infection, you should always run antivirus software that is updated with the latest signature files. Antivirus software is available from several sources. For more information, see http://www.microsoft.com/protect/computer/viruses/vista.mspx.
Use caution when opening attachments and accepting file transfers
Exercise caution with e-mail 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 web page that you are not familiar with or are suspicious of. Malicious software may be installed in your system simply by visiting a web page 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. please see our article '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 in order to compromise a system, they also attempt to exploit vulnerabilities in human behavior in order to do the same. When an attacker attempts to take advantage of human behavior in order 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 system. For more information, please see our article 'What is social engineering?'. 

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Recovery

Manual removal is not recommended for this threat. To detect and remove this threat and other malicious software that may have been installed, run a full-system scan with an up-to-date antivirus product such as the Microsoft online scanner (http://safety.live.com). For more information, see http://www.microsoft.com/protect/computer/viruses/vista.mspx.

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