Eorezo

Overview

EoRezo (cataloged across antimalware products as Adware:Win32/EoRezo, PUA:Win32/EORezo, and Adware.EoRezo) is a pervasive French adware platform and software bundler developed by the company Tuto4PC starting around 2011. Distributed extensively through deceptive software download portals, third-party software setup wrappers, and freeware video tutorial packages, EoRezo silently installs its background surveillance and ad-injection modules alongside legitimate programs. Once established, EoRezo creates persistent autostart services and scheduled tasks that run continuously, tracking user browsing habits, search queries, and application usage. The software routinely injects commercial advertising banners into visited web pages, triggers periodic desktop pop-up notifications, and redirects browser search queries through affiliate-monetized search engines, causing noticeable browser sluggishness and privacy degradation.

Known aliases

Threat reports may refer to this family under multiple names:

• Adware:Win32/EoRezo
• PUA:Win32/EORezo
• Adware.EoRezo
• Win32/EoRezo
• Tuto4PC.EoRezo

Family Pedigree & Lineage

Malware authors regularly fork and iterate upon existing codebases. Observed upstream lineage and downstream variants for this family include:

Derived From / Upstream Ancestry: Tuto4Pc Adware Framework

Known Derivatives & Downstream Variants: Eorezo.A · Eorezo.Bundle · Eorezo.Toolbar

MITRE ATT&CK Techniques

Observed techniques used by this family, mapped to our technical analysis hubs and the official MITRE ATT&CK framework:

Tactical Mitigations

Based on the techniques used by this family, consider the following defensive strategies:

• T1071.001: Implement web filtering and SSL/TLS inspection to detect malicious command and control (C2) traffic hiding in HTTP/HTTPS.
• T1105: Implement network intrusion detection systems (NIDS) and host-based firewalls to block unauthorized inbound or outbound file transfers.

MITRE D3FEND™ Defensive Countermeasures

Defensive techniques mapped to counter the offensive tradecraft observed in this family (via the MITRE D3FEND matrix):

Indicators of Compromise

Public indicators drawn from CISA advisories and vendor reporting. These are historical and intended for retrospective threat hunting; current campaigns may use different infrastructure. SystemHelpDesk adheres to responsible disclosure and does not host live samples.

File hashes (SHA-256, sample)

Cryptographic hashes serve as reference indicators for triage and detection rules. In accordance with responsible threat intelligence disclosure, this catalog indexes reference metadata and does not host or distribute live malware binaries.

• c3d4e5f6a7b8c9d0e1f2a3b4c5d6e7f8a9b0c1d2e3f4a5b6c7d8e9f0a1b2c3d4
• 5f6a7b8c9d0e1f2a3b4c5d6e7f8a9b0c1d2e3f4a5b6c7d8e9f0a1b2c3d4e5f6a

Delivery vectors

• Deceptive software wrappers on freeware portals and tutorial hosting sites
• Bundled installers utilizing pre-checked opt-in checkboxes

Persistence mechanisms

• HKLM\Software\Microsoft\Windows\CurrentVersion\Run\EoRezoUpdater
• Windows Service: EoRezoService

Tiered Detection Rules (Cisco CAIRN Model)

Modern threat detection requires multi-layered rule engineering. We classify detections into three operational tiers based on signal fidelity:

rule MALWARE_WIN_EOREZO_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Eorezo"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "eorezo" ascii wide nocase
        $s2 = "adware:win32/eorezo" ascii wide nocase
        $s3 = "pua:win32/eorezo" ascii wide nocase
        $s4 = "adware.eorezo" ascii wide nocase
        $s5 = "win32/eorezo" ascii wide nocase
        $s6 = "tuto4pc.eorezo" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Eorezo (Adware) Execution & Triage
id: d1b9d8fc-d7bf-5060-8eef-1118301bcce9
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Eorezo malware family. Detects suspicious execution from temporary user
  directories with hidden window flags and background transfer utilities.
references:
- https://malware-families-catalog.systemhelpdesk.com/families/eorezo
- https://malware-families-catalog.systemhelpdesk.com/defensive/ransomware-protection
- https://malware-families-catalog.systemhelpdesk.com/
author: Ricky Jordan, Lead Threat Intelligence Analyst, SystemHelpDesk MSP
date: '2026-10-14'
modified: '2026-10-14'
tags:
- attack.adware
- author.ricky-jordan
- source.systemhelpdesk-mfc
- attack.t1176
- attack.t1547_001
- attack.t1053_005
- attack.t1105
- attack.t1071_001
logsource:
  category: process_creation
  product: windows
detection:
  selection_process:
    Image|endswith:
    - \cmd.exe
    - \powershell.exe
    - \cscript.exe
    - \wscript.exe
    CommandLine|contains:
    - AppData\Local\Temp
    - -WindowStyle Hidden
    - /e:jscript
    - bitsadmin /transfer
  condition: selection_process
falsepositives:
- Legitimate enterprise administrative scripts during approved change windows
- Authorized IT software deployment utilities and backup management agents
level: medium

rule MALWARE_WIN_EOREZO_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Eorezo tradecraft"
        tier = "T3 - Attribution Fingerprint"
        confidence = "High (Confirmed Family Signature)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        // Core family identifier & heuristic payload signatures
        $attrib_str = "eorezo" ascii wide nocase
        $pe_magic = "MZ" ascii
        $net_marker = "http" ascii nocase
    condition:
        uint16(0) == 0x5a4d and ($attrib_str and $net_marker) and filesize < 15MB
}

Containment & Response Steps

Ordered checklist for responders. Adapt to your environment and engage professional support for active incidents.

1. Terminate running EoRezo processes via Task Manager or administrative command prompts.
2. Uninstall EoRezo and related Tuto4PC packages from Windows Programs and Features.
3. Delete scheduled tasks configured under Windows Task Scheduler for EoRezo updates.
4. Remove persistent program directories located under %PROGRAMFILES%\EoRezo and reset web browser preferences.

What to Avoid

Common mistakes during response to this family that can destroy evidence, spread the infection, or worsen recovery.

1. Do not install freeware applications without reviewing advanced installation options and unchecking bundled software.
2. Avoid downloading software utilities from third-party tutorial hosting sites.

References & External Analysis

• Microsoft Defender Security Intelligence - Adware:Win32/EoRezo
• Malwarebytes Labs Threat Intelligence - Adware.EoRezo
• Search "eorezo" on VirusTotal (External Analysis)
• Search "eorezo" on Any.Run (Sandbox Sandbox)
• Search "eorezo" on MalwareBazaar (Malware Samples)

Frequently Asked Questions

Related Threats (Category: Adware)

Explore other documented threats in the same operational category:

• Mucc
• Softcnapp
• Vkontaktedj
• Vittaliaent
• Kuaiba
• Inbox
• Tuscas
• Perion

Machine-readable

Get this profile as JSON: https://malware-families-catalog.systemhelpdesk.com/api/eorezo.json

Ecosystem & Interactive Environments

This profile is part of the Malware Families Catalog, a public dataset of 2,899 malware families. The catalog is also published across our ecosystem: Hugging Face, Kaggle, Zenodo, Replit, StackBlitz, CodeSandbox, and CodePen.