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Aliases: TrojanDownloader:Win32/Obvod.M (Microsoft), Backdoor.Win32.PcClient.foss (Kaspersky), RDN/Downloader.a!ok (McAfee)
Malware type: Trojan
Destructive: No
Platform: Windows 2000, Windows Server 2003, Windows XP (32-bit, 64-bit), Windows Vista (32-bit, 64-bit), Windows 7 (32-bit, 64-bit)
In the wild: Yes


Infection Channel: Downloaded from the Internet, Dropped by other malware

This Trojan arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It uses the Windows Task Scheduler to add a scheduled task that executes the copies it drops.

Technical Details

File size: 255,082 bytes
File type: EXE
Memory resident: No
Initial samples received date: 23 Jan 2014
Payload: Connects to URLs/IPs

Arrival Details

This Trojan arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.


This Trojan drops the following file(s)/component(s):

  • %Windows%\Tasks\At{1-240}.job

(Note: %Windows% is the Windows folder, which is usually C:\Windows.)

It drops the following copies of itself into the affected system:

  • %All Users Profile%\{random}.exe
  • %All Users Profile%\Application Data\{random}.exe
  • %AppDataLocal%\{random}.exe
  • %System%\{random}.com
  • %User Profile%\{random}.com
  • %Windows%\Fonts\{random}.com

It uses the Windows Task Scheduler to add a scheduled task that executes the copies it drops.

It injects codes into the following process(es):

  • iexplore.exe

Autostart Technique

The scheduled task executes the malware every:

  • hour

Other System Modifications

This Trojan adds the following registry entries:

Internet Explorer\Main
DisableScriptDebuggerIE = "yes"

Internet Explorer\Main
Error Dlg Displayed On Every Error = "no"

Internet Explorer\Main
NoProtectedModeBanner = "1"

Windows\CurrentVersion\Internet Settings
WarnOnZoneCrossing = "0"

Windows\CurrentVersion\Internet Settings\
2500 = "3"

LA = "609"


This Trojan checks all data in the registry entries of the following registry keys:


From the gathered data, it identifies all files with extensions .exe and .com. It renames all files it finds using the following format:

  • {file name}{space}.{exe or com}

It then creates copies of itself using the original file names and in the original folders of the renamed files.

This Trojan connects to the following sites to obtain a list of URLs for pay-per-click scheme:

  • ooo.{BLOCKED}
  • abc.{BLOCKED}
  • def.{BLOCKED}


Minimum scan engine: 9.700
First VSAPI Pattern File: 10.524.04
First VSAPI Pattern Release Date: 06 Jan 2014
VSAPI OPR Pattern Version: 10.525.00
VSAPI OPR Pattern Release Date: 07 Jan 2014

Step 1

Before doing any scans, Windows XP, Windows Vista, and Windows 7 users must disable System Restore to allow full scanning of their computers.

Step 2

Scan your computer with your Trend Micro product and note files detected as TROJ_OBVOD.AY

Step 3

Restart in Safe Mode

[ Learn more ]

Step 4

Search and delete this file

[ Learn more ]
There may be some files that are hidden. Please make sure you check the Search Hidden Files and Folders checkbox in the "More advanced options" option to include all hidden files and folders in the search result.
  • %Windows%\Tasks\At{1-240}.job

Step 5

Delete this registry value

[ Learn more ]

Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.

  • In HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main
    • DisableScriptDebuggerIE = "yes"
  • In HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main
    • Error Dlg Displayed On Every Error = "no"
  • In HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main
    • NoProtectedModeBanner = "1"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings
    • WarnOnZoneCrossing = "0"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings\Zones\3
    • 2500 = "3"
    • LA = "609"

Step 6

Restart in normal mode and scan your computer with your Trend Micro product for files detected as TROJ_OBVOD.AY. If the detected files have already been cleaned, deleted, or quarantined by your Trend Micro product, no further step is required. You may opt to simply delete the quarantined files. Please check this Knowledge Base page for more information.



  • After restarting in Safe Mode, check the list of files detected as TROJ_OBVOD.AY. These are the files noted in Step 2.
  • Open the folder location of the first file.
  • Delete the file detected as TROJ_OBVOD.AY. Note that the folder may contain two files that has almost similar file names, one of which is detected as TROJ_OBVOD.AY. If a file with file name {file name}{space}.{exe or com} exists in the current folder, rename it to {file name}.{exe or com} by removing the extra space.
  • Repeat these steps for the other files detected as TROJ_OBVOD.AY.

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Analysis By: Automation
Modified By: Jaime Benigno Reyes

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