{
  "family": "idlecrawler",
  "sample_count": 1,
  "category": "advanced_threat",
  "description": "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.<br><br><b>Understanding Idlecrawler (Idle-Time Execution)</b><br>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.<br><br><b>Execution and Evasion Mechanics</b><br>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.<br><br><b>Indicators of Compromise & Impact</b><br>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.",
  "cta": "Published by the SystemHelpdesk team.",
  "aliases": [],
  "enrichment_level": "expert-seo",
  "faq": [],
  "faq_count": 0,
  "mitre_attack": [
    "T1489",
    "T1564.001",
    "T1496"
  ],
  "cisa_advisory": null,
  "last_updated": "2026-06-09",
  "mitre_attack_detail": [
    {
      "id": "T1489",
      "name": "Service Stop (In reverse, pausing operations to evade detection when the user returns)",
      "tactic": "Defense Evasion"
    },
    {
      "id": "T1564.001",
      "name": "Hide Artifacts: Hidden Window (Spawning invisible browsers for ad fraud)",
      "tactic": "Defense Evasion"
    },
    {
      "id": "T1496",
      "name": "Resource Hijacking (Using idle CPU cycles for unauthorized cryptomining)",
      "tactic": "Impact"
    }
  ],
  "containment_steps": [
    "Use a reputable anti-malware tool to locate and remove the Idlecrawler executable and its associated persistence mechanisms.",
    "Review the Task Scheduler for any tasks configured to trigger specifically on system 'Idle' states.",
    "Implement EDR policies to detect and alert on hidden browser instances or known mining binaries executing in the background.",
    "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": [
    "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.",
    "Avoid leaving endpoints logged in and unlocked indefinitely."
  ],
  "target_industries": [
    "Global / Opportunistic"
  ],
  "motivation": "Opportunistic",
  "threat_actors": [
    "Unknown / Cybercriminal"
  ],
  "target_geographies": [
    "Global"
  ]
}