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This backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.
It executes commands from a remote malicious user, effectively compromising the affected system. It connects to a website to send and receive information.
This backdoor drops the following files:
It creates the following folders:
Other System Modifications
This backdoor deletes the following files:
(Note: %System% is the Windows system folder, which is usually C:\Windows\System32.)
It adds the following registry entries:
HKEY_CLASSES_ROOT\exefileNeverShowExt = "0"
It modifies the following registry entries:
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\AdvancedHidden = "0"
(Note: The default value data of the said registry entry is 1.)
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\AdvancedHideFileExt = "1"
(Note: The default value data of the said registry entry is 0.)
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Advanced\Folder\Hidden\SHOWALLCheckValue = "0"
This backdoor executes the following commands from a remote malicious user:
It connects to the following websites to send and receive information:
It renames the file %System%\winmm.dll to %System%\winmm16.dll. It then drops a copy of itself as %System%\winmm.dll.
It renames the file %System%\winmm.DLL to %System%\winmm16.DLL then drops a copy of itself as %System%\winmm.DLL.
This backdoor copies files with the following format below from removable drives connected through the machine:
This will be saved in the folder %SystemRoot%\$NtUninstallKB080515$, which can be retrieved later via remote commands.
Before doing any scans, Windows XP, Windows Vista, and Windows 7 users must disable System Restore to allow full scanning of their computers.
Delete this registry value
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.
To delete the registry value this malware created:
Restore this modified registry value
To restore the registry value this malware/grayware modified:
Search and delete these folders
To delete malware/grayware/spyware folders:
Scan your computer with your Trend Micro product to delete files detected as BKDR_TENGO.A. 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.
Restore this file from backup only Microsoft-related files will be restored. If this malware/grayware also deleted files related to programs that are not from Microsoft, please reinstall those programs on you computer again.
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