Extcrome

Overview

Adware:Win32/Extcrome is an intrusive Potentially Unwanted Program (PUP) categorized as a malicious Browser Extension, specifically targeting Google Chrome. It forcibly alters a user's web browsing experience by manipulating browser settings, injecting unwanted advertisements into webpages, and tracking user browsing behavior to generate illicit Pay-Per-Click (PPC) revenue for its creators.

Understanding Extcrome
To an end-user, Extcrome manifests as a sudden influx of unremovable toolbars, persistent pop-up ads, and the forced redirection of their default search engine to a low-quality, third-party portal. For a security team, it represents a breakdown in endpoint hygiene and a potential vector for more serious infections via malvertising (malicious advertisements) (`T1189`).

Execution and Hijacking Mechanics
Extcrome is typically distributed via deceptive software bundles, fake software updates, or by tricking the user on malicious download portals. Upon execution, it modifies the Windows Registry (`T1112`) and browser configuration files (like Chrome's `Preferences` file) to force-install the extension (`T1176`). To ensure the hijacking cannot be easily reversed, it often installs a persistent scheduled task or Windows Service (`T1543.003`) acting as a 'watchdog'. This watchdog monitors the browser settings; if the user attempts to remove the extension or reset their homepage, the watchdog instantly re-installs Extcrome and reverts the settings back to the hijacked state.

Indicators of Compromise & Impact
The impact is a severely degraded user experience, potential privacy violations (tracking of search queries), and exposure to potentially malicious ads. Host-based IoCs include EDR alerts for modifications to browser shortcut properties, unexpected additions to Chrome's `Extensions` directory (`%LocalAppData%\Google\Chrome\User Data\Default\Extensions`), or anomalous watchdog executables running from `%AppData%`. Network IoCs include DNS queries resolving to adware tracking infrastructure and redirected search traffic.

MITRE ATT&CK Techniques

Observed techniques used by this family, mapped to the MITRE ATT&CK framework:

Generated Detections (Boilerplate)

These YARA and Sigma rules are auto-generated based on the family name and aliases. They must be heavily tuned before deployment in a production environment.

YARA Rule

rule MALWARE_WIN_EXTCROME {
    meta:
        description = "Detects Extcrome (advanced_threat)"
        author = "SystemHelpdesk Boilerplate Generator"
        date = "2026-07-06"
    strings:
        $s1 = "extcrome" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

Sigma Rule

title: Suspicious Extcrome Activity
id: 777957cb86663156f977a7da42652398
status: experimental
description: Detects generic indicators of the extcrome malware family.
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith:
            - '\cmd.exe'
            - '\powershell.exe'
        CommandLine|contains:
            - "*extcrome*"
    condition: selection
level: medium

Containment & Response Steps

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

1. Boot the infected machine into 'Safe Mode' to prevent the Extcrome watchdog process from loading and reverting your cleanup efforts.
2. Use the Windows Control Panel to uninstall the explicitly named adware program and the freeware application that originally bundled it.
3. Manually remove the malicious extension folder from Chrome's AppData directory and reset the browser to default settings.
4. Run a thorough scan with an enterprise-grade Adware/PUA removal tool to clean up deep registry persistence mechanisms.

What to Avoid

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

1. Do not simply change the homepage back manually in Chrome; the persistent watchdog task will revert it on the next launch.
2. Avoid allowing users to download software or browser extensions from unverified third-party portals.

References & External Analysis

• Search "extcrome" on VirusTotal (External Analysis)

Frequently Asked Questions

Related Families (Category: advanced_threat)

Explore other malware families in the same category:

• Singleclickoptimizer
• Predator
• Instmonster
• Dovs
• Kgbspy

Machine-readable

Get this profile as JSON: https://jordan123234-malware-families-explorer.static.hf.space/api/extcrome.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.