Idlecrawler

Overview

Adware/Bot:Win32/Idlecrawler is a sneaky class of malware designed to exploit system resources or display advertisements exclusively when the user is not actively interacting with the computer (`T1489`). Its primary goal is monetization, either through invisible ad impressions (click fraud) or by utilizing the CPU/GPU for cryptomining, while avoiding detection by the user.

Understanding Idlecrawler (Idle-Time Execution)
To an end-user, the computer might seem perfectly fine while they are working, but the fans may spin up and the system may become unresponsive if left alone for a few minutes. For a security team, Idlecrawler represents a sophisticated evasion technique; the malware actively monitors user input (mouse movement, keystrokes) to determine when it is safe to execute its heavy payload.

Execution and Evasion Mechanics
Idlecrawler is typically distributed via software bundles or malicious browser extensions. Upon execution, it establishes persistence via Scheduled Tasks or Registry Run keys. It relies heavily on Windows APIs (like `GetLastInputInfo`) to monitor system idle time (`T1489`). When the idle threshold is met (e.g., 5 minutes of inactivity), the malware spawns a hidden browser window (`T1564.001`) to perform click fraud, or launches a mining process (`T1496`). As soon as the user moves the mouse or presses a key, Idlecrawler immediately suspends or kills the resource-intensive process to remain undetected.

Indicators of Compromise & Impact
The impact includes degraded hardware lifespan, wasted electricity, and potential exposure to secondary malware via the hidden ad networks. Host-based IoCs include EDR alerts for rapid process creation/termination correlated with user inactivity, and the presence of hidden `chrome.exe` or `iexplore.exe` processes running as background tasks rather than interactive applications. Network IoCs include bursts of traffic to advertising networks or mining pools that only occur when the workstation is locked or idle.

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

Sigma Rule

title: Suspicious Idlecrawler Activity
id: 2683afa3fe5c26a4ab529573e0884b07
status: experimental
description: Detects generic indicators of the idlecrawler malware family.
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith:
            - '\cmd.exe'
            - '\powershell.exe'
        CommandLine|contains:
            - "*idlecrawler*"
    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 reputable anti-malware tool to locate and remove the Idlecrawler executable and its associated persistence mechanisms.
2. Review the Task Scheduler for any tasks configured to trigger specifically on system 'Idle' states.
3. Implement EDR policies to detect and alert on hidden browser instances or known mining binaries executing in the background.
4. Ensure endpoints are configured to sleep or lock automatically after a short period of inactivity, which can disrupt some idle-based malware.

What to Avoid

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

1. Do not rely solely on the Windows Task Manager to find the malware; it will likely hide itself as soon as you open the Task Manager to look for it.
2. Avoid leaving endpoints logged in and unlocked indefinitely.

References & External Analysis

• Search "idlecrawler" on VirusTotal (External Analysis)

Frequently Asked Questions

Related Families (Category: advanced_threat)

Explore other malware families in the same category:

• Gemius
• Mycleanpc
• Npack
• Dropware
• Gamebox

Machine-readable

Get this profile as JSON: https://jordanricky1604-ship-it.github.io/malware-families-catalog/api/idlecrawler.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.