1. Symantec/
  2. Security Response/
  3. Trojan.Dozer


Risk Level 1: Very Low

July 8, 2009
July 11, 2009 1:47:04 AM
Infection Length:
67,072 bytes
Systems Affected:
The Trojan arrives in an email attachment and is then dropped by W32.Dozer as the following file:

It opens a back door by connecting to the following IP addresses through the following ports:
  • through TCP port 53
  • through TCP port 80
  • through TCP port 443

It then receives commands, allowing the remote attacker to perform any of the following actions:
  • Show the status of DDoS attack
  • Update itself
  • Download and execute additional files
  • Perform any of the following types of DDoS attacks against predetermined sites:
    • HTTP protocol session with GET or POST
    • TCP ACK
    • TCP SYN
    • UDP
    • ICMP

The Trojan then downloads the following configuration file:

The downloaded configuration file currently contains the following list of targeted locations:
  • www.president.go.kr
  • www.mnd.go.kr
  • www.mofat.go.kr
  • www.assembly.go.kr
  • www.usfk.mil
  • blog.naver.com
  • mail.naver.com
  • banking.nonghyup.com
  • ezbank.shinhan.com
  • ebank.keb.co.kr
  • www.hannara.or.kr
  • www.chosun.com
  • www.auction.co.kr
  • www.whitehouse.gov
  • www.faa.gov
  • www.dhs.gov
  • www.state.gov
  • www.voanews.com
  • www.defenselink.mil
  • www.nyse.com
  • www.nasdaq.com
  • finance.yahoo.com
  • www.usauctionslive.com
  • www.usbank.com
  • www.washingtonpost.com
  • www.ustreas.gov

The Trojan downloads component files from a remote location. It then uses the component files to replace the master boot record (MBR) on all attached drives with the following text
Memory of the Independence Day to prevent the compromised computer from restarting.

The Trojan then searches for files with the following extensions on all drives:

  • .accdb
  • .alz
  • .asp
  • .aspx
  • .c
  • .cpp
  • .db
  • .dbf
  • .doc
  • .docm
  • .docx
  • .eml
  • .gho
  • .gul
  • .gz
  • .hna
  • .hwp
  • .java
  • .jsp
  • .kwp
  • .mdb
  • .pas
  • .pdf
  • .php
  • .ppt
  • .pptx
  • .pst
  • .rar
  • .rtf
  • .txt
  • .wpd
  • .wpx
  • .wri
  • .xls
  • .xlsx
  • .xml
  • .zip

If the search is successful, the Trojan deletes any files found with the following properties:

  • file size of zero bytes
  • files it cannot open

It also overwrites the first five megabytes of any files found with zeros or the whole file if less than five megabytes.

The Trojan password protects any files found that are less than five megabytes by preforming the following actions:

  • Adds a random character password to the file
  • Adds a .gz extension to the file

Finally, the Trojan deletes the first megabyte of each physical drive to disable the boot sector of the first partition of each drive on the compromised computer, making recovery of the partition table difficult and then the Trojan deletes itself.


Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

  • Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
  • Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
  • Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
  • Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
  • Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
  • Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
  • If a threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
  • Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services.
  • Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
  • Isolate compromised computers quickly to prevent threats from spreading further. Perform a forensic analysis and restore the computers using trusted media.
  • Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.
  • If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
  • For further information on the terms used in this document, please refer to the Security Response glossary.
Writeup By: Mario Ballano, Liam O Murchu, Kazumasa Itabashi, and Mircea Ciubotariu
Summary| Technical Details| Removal

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