Analysis by: Jennifer Gumban
ALIASES:

Backdoor:Win32/Kelihos (Microsoft), Trojan-PSW.Win32.Tepfer.ppak (Kaspersky)

 PLATFORM:

Windows 2000, Windows Server 2003, Windows XP (32-bit, 64-bit), Windows Vista (32-bit, 64-bit), Windows 7 (32-bit, 64-bit)

 OVERALL RISK RATING:
 DAMAGE POTENTIAL:
 DISTRIBUTION POTENTIAL:
 REPORTED INFECTION:
 INFORMATION EXPOSURE:

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

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

It drops copies of itself into all the removable drives connected to an affected system.

It modifies the Internet Explorer Zone Settings.

  TECHNICAL DETAILS

File Size: 1,121,933 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 10 Sep 2013

Arrival Details

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

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
NetworkChecker = "{Original File Path}\porn.exe"

Propagation

This worm drops copies of itself into all the removable drives connected to an affected system.

Web Browser Home Page and Search Page Modification

This worm modifies the Internet Explorer Zone Settings.

Other Details

This worm connects to the following possibly malicious URL:

  • http://{BLOCKED}g.cc/
  • http://{BLOCKED}op.com
  • http://da5df6.{BLOCKED}j.com/calc.exe

NOTES:
It hides the original copy of itself after renaming it to "porn.exe".

  SOLUTION

Minimum Scan Engine: 9.300
FIRST VSAPI PATTERN FILE: 10.290.03
FIRST VSAPI PATTERN DATE: 16 Aug 2013
VSAPI OPR PATTERN File: 10.291.00
VSAPI OPR PATTERN Date: 17 Aug 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

Restart in Safe Mode

[ Learn More ]

Step 3

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
    • NetworkChecker = "{Original File Path}\porn.exe"

Step 4

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