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Win32/Bamital


Win32/Bamital is a family of malware that intercepts web browser traffic and prevents access to certain security-related websites by modifying the Hosts file. Bamital variants may also modify certain legitimate Windows files in order to execute their payload.

In the wild, the Bamital family has been used to perpetrate click-fraud.



What to do now

To detect and remove this threat and other malicious software that may be installed on your computer, run a full-system scan with an appropriate, up-to-date, security solution. The following Microsoft products detect and remove this threat:

For more information on antivirus software, see http://www.microsoft.com/windows/antivirus-partners/.

This malware creates entries in the Hosts file to prevent access to certain websites. To recreate a clean Hosts file, please refer to the following article:

Threat behavior

Win32/Bamital is a family of malware that intercepts web browser traffic and prevents access to certain security-related websites by modifying the Hosts file. Bamital variants may also modify certain legitimate Windows files in order to execute their payload.

Installation

Win32/Bamital may be dropped and loaded into "spoolsv.exe" by TrojanDropper:Win32/Bamital.D.

Win32/Bamital tries to connect to a remote server to report infection of the affected computer.

Payload

Redirects user searches

Win32/Bamital connects to a remote host to obtain configuration data. The data contains destination hosts, which are used when redirecting browser searches performed by the user with Google, Yahoo!, or Bing.

Intercepts web traffic

Win32/Bamital tries to inject its code into running web browser processes, for example, "iexplore.exe", "firefox.exe" and "opera.exe" in order to intercept web browser traffic and redirect search engine results.

Modifies Hosts file

Win32/Bamital modifies the Windows Hosts file. The local Hosts file overrides the DNS resolution of a website URL to a particular IP address. Malicious software may make modifications to the Hosts file to redirect specified URLs to different IP addresses. Malware often modifies a computer's Hosts file to stop users from accessing websites associated with particular security-related applications (such as antivirus for example). Win32/Bamital may redirect the following hosts in order to prevent affected users from accessing them:

  • ahnlab.com
  • akamai.avg.com
  • aladdin.com
  • anti-virus.by
  • antivir.es
  • antiy.net
  • authentium.com
  • avast.com
  • avg.com
  • avp.com
  • avp.ru
  • avpg.crsi.symantec.com
  • backup.avg.cz
  • bancoguayaquil.com
  • bcpzonasegura.viabcp.com
  • bitdefender.com
  • clamav.net
  • comodo.com
  • customer.symantec.com
  • dispatch.mcafee.com
  • download.mcafee.com
  • download.microsoft.com
  • downloads.microsoft.com
  • downloads1.kaspersky-labs.com
  • downloads2.kaspersky-labs.com
  • downloads3.kaspersky-labs.com
  • downloads4.kaspersky-labs.com
  • downloads5.kaspersky-labs.com
  • drweb.com
  • emsisoft.com
  • eset.com
  • eset.es
  • f-prot.com
  • f-secure.com
  • fortinet.com
  • gdata.es
  • go.microsoft.com
  • grisoft.com
  • hacksoft.com.pe
  • ikarus.at
  • kaspersky-labs.com
  • kaspersky.com
  • kaspersky.ru
  • liveupdate.symantec.com
  • liveupdate.symantecliveupdate.com
  • macafee.com
  • mast.mcafee.com
  • mcafee.com
  • microsoft.com
  • msdn.microsoft.com
  • my-etrust.com
  • networkassociates.com
  • nod32.com
  • norman.com
  • norton.com
  • nprotect.com
  • pandasecurity.com
  • pandasoftware.com
  • pctools.com
  • pif.symantec.com
  • pifmain.symantec.com
  • rads.mcafee.com
  • rising-global.com
  • scanner.novirusthanks.org
  • secure.nai.com
  • securityresponse.symantec.com
  • service1.symantec.com
  • sophos.com
  • sunbeltsoftware.com
  • support.microsoft.com
  • symantec.com
  • threatexpert.com
  • trendmicro.com
  • u2.eset.com
  • u20.eset.com
  • u3.eset.com
  • u4.eset.com
  • u7.eset.com
  • update.avg.com
  • update.microsoft.com
  • update.symantec.com
  • updates.symantec.com
  • updates1.kaspersky-labs.com
  • updates2.kaspersky-labs.com
  • updates3.kaspersky-labs.com
  • us.mcafee.com
  • viabcp.com
  • virscan.org
  • virusbuster.hu
  • viruslist.com
  • viruslist.ru
  • virusscan.jotti.org
  • virustotal.com
  • windowsupdate.microsoft.com

Modifies Windows files

Some variants of Win32/Bamital attempt to modify the following legitimate Windows files:

  • winlogon.exe
  • explorer.exe

Detection for the modified files are detected as variants of Virus:Win32/Bamital.

Note: The original copies of "explorer.exe" and "winlogon.exe" are saved to "%windir%\temp" by the virus as "explorer.dat" and "winlogon.dat" respectively.

The modified system files attempt to load a single DLL file. Possible file names for the loaded file include:

  • <system folder>\kb.dll,
  • <system folder>\ms.dll,
  • <system folder>\nt.dll,
  • <system folder>\zx.dll,
  • <system folder>\k.dll ,
  • <system folder>\b.dll ,
  • <system folder>\w.dll ,

This DLL file is used to load a data file, for example "c: \windows\sytem32\hlp", which contains the bulk of the Win32/Bamital payload. The data file is detected as Trojan:Win32/Bamital.

Analysis by Scott Molenkamp


Symptoms

System changes

The following system changes may indicate the presence of this malware:

  • Attempts to access the following servers, for example via your browser or an antivirus program, fail:
    • ahnlab.com
    • akamai.avg.com
    • aladdin.com
    • anti-virus.by
    • antivir.es
    • antiy.net
    • authentium.com
    • avast.com
    • avg.com
    • avp.com
    • avp.ru
    • avpg.crsi.symantec.com
    • backup.avg.cz
    • bancoguayaquil.com
    • bcpzonasegura.viabcp.com
    • bitdefender.com
    • clamav.net
    • comodo.com
    • customer.symantec.com
    • dispatch.mcafee.com
    • download.mcafee.com
    • download.microsoft.com
    • downloads.microsoft.com
    • downloads1.kaspersky-labs.com
    • downloads2.kaspersky-labs.com
    • downloads3.kaspersky-labs.com
    • downloads4.kaspersky-labs.com
    • downloads5.kaspersky-labs.com
    • drweb.com
    • emsisoft.com
    • eset.com
    • eset.es
    • f-prot.com
    • f-secure.com
    • fortinet.com
    • gdata.es
    • go.microsoft.com
    • grisoft.com
    • hacksoft.com.pe
    • ikarus.at
    • kaspersky-labs.com
    • kaspersky.com
    • kaspersky.ru
    • liveupdate.symantec.com
    • liveupdate.symantecliveupdate.com
    • macafee.com
    • mast.mcafee.com
    • mcafee.com
    • microsoft.com
    • msdn.microsoft.com
    • my-etrust.com
    • networkassociates.com
    • nod32.com
    • norman.com
    • norton.com
    • nprotect.com
    • pandasecurity.com
    • pandasoftware.com
    • pctools.com
    • pif.symantec.com
    • pifmain.symantec.com
    • rads.mcafee.com
    • rising-global.com
    • scanner.novirusthanks.org
    • secure.nai.com
    • securityresponse.symantec.com
    • service1.symantec.com
    • sophos.com
    • sunbeltsoftware.com
    • support.microsoft.com
    • symantec.com
    • threatexpert.com
    • trendmicro.com
    • u2.eset.com
    • u20.eset.com
    • u3.eset.com
    • u4.eset.com
    • u7.eset.com
    • update.avg.com
    • update.microsoft.com
    • update.symantec.com
    • updates.symantec.com
    • updates1.kaspersky-labs.com
    • updates2.kaspersky-labs.com
    • updates3.kaspersky-labs.com
    • us.mcafee.com
    • viabcp.com
    • virscan.org
    • virusbuster.hu
    • viruslist.com
    • viruslist.ru
    • virusscan.jotti.org
    • virustotal.com
    • windowsupdate.microsoft.com
  • The presence of the following files:
    explorer.dat
    winlogon.dat

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 webpages.
  • Avoid downloading pirated software.
  • Protect yourself against social engineering attacks.
  • 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. Instructions on how to download the latest versions of some common software is available from the following:

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

Most antivirus software can detect and prevent infection by known malicious software. To help protect you from infection, you should always run antivirus software, such as Microsoft Security Essentials, that is updated with the latest signature files. For more information, see http://www.microsoft.com/windows/antivirus-partners/.

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 webpages

Exercise caution with links to webpages 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.


Alert level: Severe
This entry was first published on: May 27, 2011
This entry was updated on: Feb 07, 2013

This threat is also detected as:
No known aliases