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Aliases: Trojan:Win32/Medfos.A (Microsoft); (McAfee); Trojan.Malcol (Symantec); Trojan.Win32.Midhos.vbp (Kaspersky); Trojan.Win32.Medfos.t (v) (Sunbelt); Win32/Cryptor (AVG)
Malware type: Trojan
Destructive: No
Platform: Windows 2000, Windows XP, Windows Server 2003
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.

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.

Other System Modifications

This Trojan adds the following registry entries:

Chrome\Extensions\{random characters}
path = %User Profile%\Application Data\{random characters}.crx

Dropping Routine

This Trojan drops the following files:

  • %User Profile%\Application Data\{random numbers}.crx
  • %User Profile%\Application Data\dfsong.dll

(Note: %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003, or C:\Users\{user name} on Windows Vista and 7.)

This report is generated via an automated analysis system.

Minimum scan engine: 9.300

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 malware/grayware files dropped/downloaded by TROJ_MEDFOS.SMI

    • %User Profile%\Application data\{random characters}.crx
    • %User Profile%\Application Data\dfsong.dll

Step 3

Delete this registry key

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. Before you could do this, you must restart in Safe Mode. For instructions on how to do this, you may refer to this page If the preceding step requires you to restart in safe mode, you may proceed to edit the system registry.

  • In HKEY_LOCAL_MACHINE\SOFTWARE\Google\Chrome\Extensions
    • {random characters}

Step 4

Scan your computer with your Trend Micro product to delete 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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Analysis By: Adrianne Chester Camat