The malware uses similar techniques as those of PlugX, like process injection and use of blob file. The malware directly loads the backdoor file located in its command-and-control (C&C) server. This means there are no downloaded files and file-based detection of the backdoor code is not possible.
To get a one-glance comprehensive view of the behavior of this Backdoor, refer to the Threat Diagram shown below.

This backdoor may be dropped by other malware.
It executes commands from a remote malicious user, effectively compromising the affected system.
Arrival Details
This backdoor may be dropped by the following malware:
Installation
This backdoor drops the following copies of itself into the affected system and executes them:
(Note: %System% is the Windows system folder, which is usually C:\Windows\System32.)
It drops the following file(s)/component(s):
- %Application Data%\profile.dat - blob file containing malware routines
(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Documents and Settings\{user name}\Application Data on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Roaming on Windows Vista and 7.)
It adds the following processes:
It injects itself into the following processes as part of its memory residency routine:
Autostart Technique
This backdoor adds the following registry entries to enable its automatic execution at every system startup:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
Yahoo! = ""%System%\ymsgr_tray.exe" -local"
Backdoor Routine
This backdoor executes the following commands from a remote malicious user:
- Get computer name and name of current user
- Retrieve list of local groups where the current user belongs.
- Create autorun registry entries
- Enumerate files and directories
- Get drive information
- Upload files
- Download files
- Execute files
- Download plugin and load into memory
- Enumerate processes
- Enumerate process modules
- Get process information
- Terminate processes
- Get installer properties from Uninstall Registry Key entries
- Manage files and directories (create, delete, modify, rename, search)
- Manage registries (create, delete, modify, search, view)
- Manage services (install, modify, search, start, stop, uninstall, view)
- Get service information
- Manage windows
- Perform remote shell
- Restart system
- Remove self from system
- Update self and configuration
- Enumerate TCP and UDP connection states
It connects to the following URL(s) to send and receive commands from a remote malicious user:
- {BLOCKED}805.{BLOCKED}y.net
NOTES:
The malware needs the following command line parameters in order to perform its intended routine:
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
Remove the malware/grayware file that dropped/downloaded BKDR_RARSTONE.A
Step 3
Restart in Safe Mode
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To restart in Safe Mode:
• For Windows 2000 users
- Restart your computer.
- Press F8 when you see the Starting Windows bar at the bottom of the screen.
- Choose the Safe Mode option from the Windows Advanced Options menu then press Enter.
• For Windows XP users
- Restart your computer.
- Press F8 after the Power-On Self Test (POST) routine is done. If the Windows Advanced Options menu does not appear, try restarting then pressing F8 several times when the POST screen appears.
- Choose the Safe Mode option from the Windows Advanced Options menu then press Enter.
• For Windows Server 2003 users
- Restart your computer.
- Press F8 after Windows starts up. If the Windows Advanced Options menu does not appear, try restarting again and pressing F8 several times afterward.
- On the Windows Advanced Option menu, use the arrow keys to select Safe Mode then press Enter.
• For Windows Vista and Windows 7 users
- Restart your computer.
- Press F8 after the Power-On Self Test (POST) routine is done. If the Advanced Boot Options menu does not appear, try restarting and then pressing F8 several times after the POST screen is displayed.
- On the Advanced Boot Options menu, use the arrow keys to select the Safe Mode option, and then press Enter.
Step 4
Delete this registry value
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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_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
- Yahoo! = ""%System%\ymsgr_tray.exe" -local"
To delete the registry value this malware/grayware created:
- Open Registry Editor. Click Start>Run, type REGEDIT, then press Enter.
- In the left panel, double-click the following:
HKEY_LOCAL_MACHINE>SOFTWARE>Microsoft>Windows>CurrentVersion>Run - In the right panel, locate and delete the entry:
Yahoo! = ""%System%\ymsgr_tray.exe" -local" - Close Registry Editor.
Step 5
Search and delete this file
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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.
- %Application Data%\profile.dat
To manually delete a malware/grayware file from an affected system:
• For Windows 2000, Windows XP, and Windows Server 2003:
- Right-click Start then click Search....
- In the left panel, click All Files.
- In the Named input box, type the following:
- %Application Data%\profile.dat
- In the Look In drop-down list, select My Computer then press Enter.
- Once located, select the file then press SHIFT+DELETE to delete it.
• For Windows Vista and Windows 7 users:
- Click Start>Computer.
- In the Search input box, type the following:
- %Application Data%\profile.dat
- Once located, select the file then press SHIFT+DELETE to delete it.
*Note: Read the following Microsoft page if these steps do not work on Windows 7.
Step 6
Restart in normal mode and scan your computer with your Trend Micro product for files detected as BKDR_RARSTONE.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.
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