Analysis by: Mariefher Grace Villanueva
ALIASES:

JS:Nimda-B [Trj] (AVAST); Win32.Worm.Nimda.O (BITDEFENDER)

 PLATFORM:

Windows

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

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 requires its main component to successfully perform its intended routine.

  TECHNICAL DETAILS

File Size: 33,938 bytes
File Type: HTML, HTM
Memory Resident: Yes
Initial Samples Received Date: 24 Mar 2026

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 Details

This Trojan requires its main component to successfully perform its intended routine.

NOTES:

  • This Java Script is a component of the PE_NIMDA.A worm. It opens the README.EML file that carries the worm. It does not have a destructive payload.
  • This script does not modify any system and registry file. Its main function is to open the README.EML file that contains the PE_NIMDA.A worm.

  SOLUTION

Minimum Scan Engine: 9.850
FIRST VSAPI PATTERN FILE: 20.846.02
FIRST VSAPI PATTERN DATE: 26 Mar 2026
VSAPI OPR PATTERN File: 20.847.00
VSAPI OPR PATTERN Date: 27 Mar 2026

Step 1

Before doing any scans, Windows 7, Windows 8, Windows 8.1, and Windows 10 users must disable System Restore to allow full scanning of their computers.

Step 2

Close all opened browser windows

Step 3

Scan your computer with your Trend Micro product to delete files detected as Trojan.JS.NIMDA.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 the following Trend Micro Support pages for more information:


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