Analysis by: Francis Xavier Antazo
ALIASES:

Ransom:MSIL/Ryzerlo.A (Microsoft); a variant of MSIL/Filecoder.AK (ESET); Ransom.HiddenTear (AVG);

 PLATFORM:

Windows

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

Infection Channel: Downloaded from the Internet, Dropped by other malware

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.

  TECHNICAL DETAILS

File Size: 211,968 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 29 Sep 2016
Payload: Encrypts files, Renames files, Drops files

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.

Installation

This Trojan drops the following copies of itself into the affected system and executes them:

  • C:\ex3t.exe

It drops the following files:

  • C:\Desktop\ex3t.pdf
  • C:\ex3t.txt {contains computername and key}

It leaves text files that serve as ransom notes containing the following:

  • Files has been encrypted hcrypto

Other Details

This Trojan encrypts files with the following extensions:

  • .ex3t
  • .doc
  • .docx
  • .xls
  • .xlsx

It renames encrypted files using the following names:

  • {original filename and file extension}.hcrypto

  SOLUTION

Minimum Scan Engine: 9.800
FIRST VSAPI PATTERN FILE: 12.800.08
FIRST VSAPI PATTERN DATE: 26 Sep 2016
VSAPI OPR PATTERN File: 12.801.00
VSAPI OPR PATTERN Date: 27 Sep 2016

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

Search and delete this file

[ Learn More ]
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.  
  • C:\ex3t.txt
  • C:\Desktop\ex3t.pdf

Step 3

Scan your computer with your Trend Micro product to delete files detected as RANSOM_CRYPTEAR.SM0. 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.

Step 4

Restore encrypted files from backup.


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