Fleercivet

Overview

Adware:Win32/Fleercivet is a persistent adware family focused on click fraud and silent ad-injection. Unlike traditional adware that constantly bothers the user with visible pop-ups, Fleercivet is designed to operate more stealthily, generating revenue by simulating clicks on background advertisements or by quietly replacing legitimate ads on websites with those belonging to the attacker's affiliate network (`T1499`).

Understanding Fleercivet (Ad Injection)
To an end-user, the infection might manifest as slow browser performance or noticing that ads on familiar websites look strangely off-brand or lower quality. For a security team, Fleercivet is a network nuisance that indicates a failure in endpoint controls regarding Potentially Unwanted Programs (PUPs) and introduces the risk of malvertising.

Execution and Injection Mechanics
Fleercivet is distributed primarily via software bundling. Upon execution, it establishes persistence, often utilizing a Scheduled Task or modifying the `AppInit_DLLs` registry key (`T1546.010`) to ensure its DLL is loaded into every new process (specifically targeting browsers). Once hooked into the browser process (Chrome, Firefox, or Edge), Fleercivet uses Man-in-the-Browser (MitB) techniques to intercept web traffic. It parses the HTML of incoming web pages and dynamically injects its own JavaScript, which replaces existing ad banners or creates invisible iframes to click on ads silently in the background.

Indicators of Compromise & Impact
The impact is degraded system performance and exposure to untrusted advertising networks. Host-based IoCs include EDR alerts for DLL injection into browser processes (e.g., `chrome.exe`), unauthorized modifications to `AppInit_DLLs`, and unexpected Scheduled Tasks. Network IoCs include DNS requests and HTTP traffic directed towards known affiliate marketing and tracking domains that occur independently of user navigation.

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

Sigma Rule

title: Suspicious Fleercivet Activity
id: 75eab02b8fca587ffc293d7cdc52d40a
status: experimental
description: Detects generic indicators of the fleercivet malware family.
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith:
            - '\cmd.exe'
            - '\powershell.exe'
        CommandLine|contains:
            - "*fleercivet*"
    condition: selection
level: medium

Containment & Response Steps

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

1. Use a robust anti-malware tool (like Malwarebytes or AdwCleaner) to locate and remove the Fleercivet DLLs and the associated injection registry keys.
2. Verify and clean the `AppInit_DLLs` registry key (`HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Windows`).
3. Reset all web browsers to default settings to ensure no malicious extensions were also dropped.
4. Educate users on the risks of 'Express Installations' when downloading freeware.

What to Avoid

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

1. Do not assume the browser is secure just because no new toolbars are visible; Fleercivet operates largely via injected code, not UI extensions.
2. Avoid relying solely on traditional antivirus signatures, as the ad-injection scripts are frequently updated.

References & External Analysis

• Search "fleercivet" on VirusTotal (External Analysis)

Frequently Asked Questions

Related Families (Category: advanced_threat)

Explore other malware families in the same category:

• Shopbot
• Wsgame
• Lazagne
• Qaccel
• Tdss

Machine-readable

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