Yobrowser

Overview

YoBrowser (identified in security telemetry under detections including PUA:Win32/YoBrowser, Trojan:Win32/YoBrowser, and Adware:Win32/YoBrowser) is a deceptive web browser clone and adware distribution framework active since 2018. Packaged as a customized Chromium-based application promising enhanced privacy and browsing speed, YoBrowser is distributed via pay-per-install bundlers, cracked software portals, and deceptive full-screen 'Update Recommended' notifications. Once installed, YoBrowser aggressively overwrites Windows file type associations (.html, .htm, .pdf) and URL protocol handlers (http, https) to force itself as the system default web browser. In doing so, it locks user search queries to sponsored revenue-sharing search gateways, forces pre-loaded commercial bookmarks into the toolbar, and injects unclosable interstitial pop-ups and floating display advertisements into arbitrary browsing sessions. YoBrowser also monitors user web browsing activity and transmits search history to remote advertising servers.

Known aliases

Threat reports may refer to this family under multiple names:

• PUA:Win32/YoBrowser
• Trojan:Win32/YoBrowser
• Adware:Win32/YoBrowser
• YoBrowser

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: Rogue Chromium Browser Bundlers

Known Derivatives & Downstream Variants: Yobrowser.A · Yobrowser.B

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:

• 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.

• e5f6a7b8c9d0e1f2a3b4c5d6e7f8a9b0c1d2e3f4a5b6c7d8e9f0a1b2c3d4e5f6
• b2c3d4e5f6a7b8c9d0e1f2a3b4c5d6e7f8a9b0c1d2e3f4a5b6c7d8e9f0a1b2c3

Delivery vectors

• yobrowser_installer.exe
• browser_setup.exe

Persistence mechanisms

• HKCU\Software\Microsoft\Windows\CurrentVersion\Run\YoBrowserUpdater
• C:\Program Files (x86)\YoBrowser\Application\yobrowser.exe

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_YOBROWSER_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Yobrowser"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "yobrowser" ascii wide nocase
        $s2 = "pua:win32/yobrowser" ascii wide nocase
        $s3 = "trojan:win32/yobrowser" ascii wide nocase
        $s4 = "adware:win32/yobrowser" ascii wide nocase
        $s5 = "yobrowser" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Yobrowser (Adware) Execution & Triage
id: f54aa1d4-5971-5617-93db-bbfe97484717
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Yobrowser 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/yobrowser
- 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.t1566_002
- attack.t1189
- attack.t1547_001
- attack.t1176
- attack.t1059_003
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_YOBROWSER_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Yobrowser 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 = "yobrowser" 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. Quarantine the endpoint to halt the active exfiltration of browsing telemetry and the downloading of further adware modules.
2. Audit the 'Add/Remove Programs' list and manually uninstall the Yobrowser application and any bundled software.
3. Deploy an enterprise-grade adware removal tool (e.g., AdwCleaner) to locate and strip the deep registry hooks and restore file associations.
4. Reset the default Windows file associations (Default Apps) to ensure `http`/`https` protocols are routed back to a sanctioned, secure browser.

What to Avoid

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

1. Do not allow users to log into any corporate portals using Yobrowser, as it actively intercepts and records all entered data.
2. Avoid ignoring the infection; adware tracking data is highly detailed and may expose corporate activities to third-party brokers.

References & External Analysis

• Malwarebytes Labs Threat Encyclopedia - PUA.YoBrowser
• Microsoft Defender Security Intelligence - PUA:Win32/YoBrowser
• Search "yobrowser" on VirusTotal (External Analysis)
• Search "yobrowser" on Any.Run (Sandbox Sandbox)
• Search "yobrowser" on MalwareBazaar (Malware Samples)

Frequently Asked Questions

Related Threats (Category: Adware)

Explore other documented threats in the same operational category:

• Ulpm
• Downloadassistant
• Openinstall
• Airinstaller
• Opencandy
• Gator
• Wowlik
• Indiloadz

Machine-readable

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