{
  "family": "hacdef",
  "sample_count": 1,
  "category": "backdoor",
  "description": "Rootkit:Win32/Hacdef (Hacker Defender) is a legendary, historically significant user-mode rootkit. Wide-spread in the mid-2000s, Hacdef was one of the first sophisticated, widely available tools designed specifically to hide the presence of an attacker, their files, and their backdoor connections from the system administrator and early antivirus software (`T1014`).<br><br><b>Understanding Hacdef (User-Mode Rootkits)</b><br>To an end-user or system administrator relying on standard Windows tools (like Task Manager or `netstat`), the system appears entirely normal. Hacdef intercepts the API calls made by these tools and actively filters the results. For example, if an attacker drops a file named `evil.exe`, Hacdef ensures that when Explorer asks for a list of files, `evil.exe` is removed from the list before it reaches the screen.<br><br><b>Execution and Hooking Mechanics</b><br>Hacdef is deployed *after* an attacker has achieved administrative access. It is a user-mode rootkit, meaning it does not typically load a kernel driver (`.sys`). Instead, it uses API Hooking (`T1056.004`), specifically injecting itself into all running processes and intercepting calls to fundamental Windows APIs (like `FindNextFile`, `EnumProcesses`, `RegEnumKey`). It uses an `.ini` configuration file that tells it exactly which file names, process names, registry keys, and network ports to hide from the OS.<br><br><b>Indicators of Compromise & Impact</b><br>The impact is total loss of system integrity and a deeply hidden attacker presence. Because Hacdef hooks user-mode APIs, host-based IoCs are difficult to find with standard tools. Advanced EDR tools detect Hacdef by identifying the inline hooks placed on the API functions in memory. Another classic detection method is cross-view validation (comparing the output of a clean, low-level disk read against the output of the hooked Windows API). Network IoCs involve looking for the hidden backdoors Hacdef is protecting.",
  "cta": "Published by the SystemHelpdesk team.",
  "aliases": [],
  "enrichment_level": "expert-seo",
  "faq": [],
  "faq_count": 0,
  "mitre_attack": [
    "T1014",
    "T1056.004"
  ],
  "cisa_advisory": null,
  "last_updated": "2026-06-09",
  "mitre_attack_detail": [
    {
      "id": "T1014",
      "name": "Rootkit (The core functionality of hiding the attacker's presence)",
      "tactic": "Defense Evasion"
    },
    {
      "id": "T1056.004",
      "name": "Input Capture: Credential API Hooking (Intercepting system calls to filter output)",
      "tactic": "Credential Access"
    }
  ],
  "containment_steps": [
    "Do not attempt to clean a system infected with a rootkit using standard tools; the rootkit controls what those tools see.",
    "Boot the system from a clean, read-only environment (like an offline AV rescue disk or a Linux Live CD) to inspect the hard drive without the rootkit's interference.",
    "Analyze the `hxdef.ini` (or similarly named configuration file) to determine exactly what the attacker was hiding (e.g., hidden backdoor ports or dropped executables).",
    "The safest remediation for a confirmed rootkit infection is a complete wipe and reimage of the system from known-good media."
  ],
  "what_to_avoid": [
    "Avoid relying on `netstat` or Task Manager to investigate a suspected Hacdef infection; they are actively lying to you.",
    "Do not connect the infected machine back to the network until it has been completely wiped, as the attacker has persistent, hidden access."
  ],
  "target_industries": [
    "Global / Opportunistic"
  ],
  "motivation": "Opportunistic",
  "threat_actors": [
    "Unknown / Cybercriminal"
  ],
  "target_geographies": [
    "Global"
  ]
}