Analysis by: Adrianne Chester Camat
 Modified by: Michelle Morales


Trojan:Win32/Medfos.A (Microsoft); (McAfee); Trojan.Malcol (Symantec); Trojan.Win32.Midhos.vbp (Kaspersky); Trojan.Win32.Medfos.t (v) (Sunbelt); Win32/Cryptor (AVG)


Windows 2000, Windows XP, Windows Server 2003


  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes


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 deletes itself after execution.


File Size: 176,640 bytes
File Type: EXE
Memory Resident: No
Initial Samples Received Date: 01 Feb 2013

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.

Autostart Technique

This Trojan adds the following registry entries to enable its automatic execution at every system startup:

{random filename} = "rundll32.exe, "%Application Data%\{random filename}.dll",{export function}*"

Dropping Routine

This Trojan drops the following files:

  • %Application Data%\{random filename}.dll

(Note: %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

Other Details

This Trojan deletes itself after execution.

The exported function may be any of the following:

  • PszAllocW
  • SetColumns
  • CreateTempFile


Minimum Scan Engine: 9.300
VSAPI OPR PATTERN File: 10.479.00
VSAPI OPR PATTERN Date: 17 Dec 2013

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

Note that not all files, folders, and registry keys and entries are installed on your computer during this malware's/spyware's/grayware's execution. This may be due to incomplete installation or other operating system conditions. If you do not find the same files/folders/registry information, please proceed to the next step.

Step 3

Restart in Safe Mode

[ Learn More ]

Step 4

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_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • {random filename} = "rundll32.exe, "%Application Data%\{random filename}.dll",{export function}"

Step 5

Remove malware/grayware files dropped/downloaded by TROJ_MEDFOS.SMI. (Note: Please skip this step if the threats listed below have already been removed.)

    • %Application Data%\{random filename}.dll

Step 6

Restart in normal mode and scan your computer with your Trend Micro product for files detected as TROJ_MEDFOS.SMI. 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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