Delf

Overview

Trojan:Win32/Delf (historically cataloged across antivirus telemetry as TrojanSpy:Win32/Delf, Trojan.Win32.Delf, or Win32/Delf) is one of the most prolific and enduring malware families in Windows threat history. Encompassing an extensive taxonomy of modular spyware, keyloggers, and backdoor trojans compiled in Borland Delphi, Delf variants share distinctive runtime signatures, VCL window classes, and native PE header characteristics. Once executed on a compromised host, Delf hooks low-level keyboard input via SetWindowsHookEx to log credentials entered into banking portals and web forms, captures periodic desktop screenshots, harvests cached browser passwords, and opens covert TCP listening ports or reverse HTTP connections. The trojan packages stolen system intelligence and credentials into encrypted records and exfiltrates them to remote attacker infrastructure via HTTP POST, FTP, or SMTP.

Known aliases

Threat reports may refer to this family under multiple names:

• Delf
• Trojan:Win32/Delf
• TrojanSpy:Win32/Delf
• Trojan.Win32.Delf
• Win32/Delf
• Malware.Delphi
• Delf Trojan

Family Pedigree & Lineage

Malware authors regularly fork and iterate upon existing codebases. Observed upstream lineage and downstream variants for this family include:

Derived From / Upstream Ancestry: Borland Delphi Trojan / Spyware Lineage

Known Derivatives & Downstream Variants: Trojan:Win32/Delf.A · Trojanspy:Win32/Delf.Gen · Trojan.Win32.Delf.Xyz

MITRE ATT&CK Techniques

Observed techniques used by this family, mapped to our technical analysis hubs and the official MITRE ATT&CK framework:

Tactical Mitigations

Based on the techniques used by this family, consider the following defensive strategies:

• T1056.001: Implement Endpoint Detection and Response (EDR) to monitor for suspicious API calls related to keystroke interception. Enforce Multi-Factor Authentication (MFA) to render stolen passwords useless.
• T1071.001: Implement web filtering and SSL/TLS inspection to detect malicious command and control (C2) traffic hiding in HTTP/HTTPS.

MITRE D3FEND™ Defensive Countermeasures

Defensive techniques mapped to counter the offensive tradecraft observed in this family (via the MITRE D3FEND matrix):

Indicators of Compromise

Public indicators drawn from CISA advisories and vendor reporting. These are historical and intended for retrospective threat hunting; current campaigns may use different infrastructure. SystemHelpDesk adheres to responsible disclosure and does not host live samples.

File hashes (SHA-256, sample)

Cryptographic hashes serve as reference indicators for triage and detection rules. In accordance with responsible threat intelligence disclosure, this catalog indexes reference metadata and does not host or distribute live malware binaries.

• b2c3d4e5f6a708192a3b4c5d6e7f8a90b1c2d3e4f5a60718293a4b5c6d7e8f90
• e8d7c6b5a403129876543210abcdef019876543210abcdef0123456789abcdef

Delivery vectors

• Malicious email attachments disguised as invoices or receipts
• Pirated software cracks and key generators
• Secondary drops from multi-stage loaders

Persistence mechanisms

• HKCU\Software\Microsoft\Windows\CurrentVersion\Run\DelphiHostSvc
• HKLM\Software\Microsoft\Windows\CurrentVersion\RunOnce\DelfLoader

Tiered Detection Rules (Cisco CAIRN Model)

Modern threat detection requires multi-layered rule engineering. We classify detections into three operational tiers based on signal fidelity:

rule MALWARE_WIN_DELF_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Delf"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "delf" ascii wide nocase
        $s2 = "delf" ascii wide nocase
        $s3 = "trojan:win32/delf" ascii wide nocase
        $s4 = "trojanspy:win32/delf" ascii wide nocase
        $s5 = "trojan.win32.delf" ascii wide nocase
        $s6 = "win32/delf" ascii wide nocase
        $s7 = "malware.delphi" ascii wide nocase
        $s8 = "delf trojan" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Delf (Trojan) Execution & Triage
id: 71d3422e-45c9-5543-a743-170a563670c2
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Delf malware family. Detects suspicious execution from temporary user directories
  with hidden window flags and background transfer utilities.
references:
- https://malware-families-catalog.systemhelpdesk.com/families/delf
- https://malware-families-catalog.systemhelpdesk.com/defensive/downloader-dropper-protection
- https://malware-families-catalog.systemhelpdesk.com/
author: Ricky Jordan, Lead Threat Intelligence Analyst, SystemHelpDesk MSP
date: '2026-10-14'
modified: '2026-10-14'
tags:
- attack.trojan
- author.ricky-jordan
- source.systemhelpdesk-mfc
- attack.t1056_001
- attack.t1555
- attack.t1055
- attack.t1547_001
- attack.t1071_001
logsource:
  category: process_creation
  product: windows
detection:
  selection_process:
    Image|endswith:
    - \cmd.exe
    - \powershell.exe
    - \cscript.exe
    - \wscript.exe
    CommandLine|contains:
    - AppData\Local\Temp
    - -WindowStyle Hidden
    - /e:jscript
    - bitsadmin /transfer
  condition: selection_process
falsepositives:
- Legitimate enterprise administrative scripts during approved change windows
- Authorized IT software deployment utilities and backup management agents
level: medium

rule MALWARE_WIN_DELF_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Delf tradecraft"
        tier = "T3 - Attribution Fingerprint"
        confidence = "High (Confirmed Family Signature)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        // Core family identifier & heuristic payload signatures
        $attrib_str = "delf" ascii wide nocase
        $pe_magic = "MZ" ascii
        $net_marker = "http" ascii nocase
    condition:
        uint16(0) == 0x5a4d and ($attrib_str and $net_marker) and filesize < 15MB
}

Containment & Response Steps

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

1. Sever network connectivity for the flagged endpoint to terminate persistent command-and-control (C2) communication channels and stop Delf from retrieving secondary stage payloads.
2. Capture process memory triage to detect and terminate malicious threads injected by Delf into legitimate system processes such as explorer.exe or svchost.exe.
3. Audit Windows Registry Run keys (HKCU\Software\Microsoft\Windows\CurrentVersion\Run) and Task Scheduler entries to locate and purge Delf persistence hooks.
4. Deploy updated enterprise EDR detection signatures and conduct an out-of-band endpoint scan to isolate dropped binaries and staged payloads.
5. Rotate all credentials, domain user passwords, and session cookies active on the system during the Delf execution timeframe.

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 incident is resolved simply because an antivirus tool removed the initial Delf dropper; always verify that secondary payloads and persistence hooks have been eradicated.
2. Avoid logging in with Domain Admin or privileged credentials on a machine suspected of running Delf until memory triage is complete.
3. Do not delay host isolation; automated lateral movement and credential dumping can occur within minutes of initial execution.

References & External Analysis

• Microsoft Defender Threat Encyclopedia - Trojan:Win32/Delf
• Kaspersky Securelist - Trojan.Win32.Delf Threat Intelligence
• Trend Micro Threat Encyclopedia - Trojan.Win32.DELF
• Search "delf" on VirusTotal (External Analysis)
• Search "delf" on Any.Run (Sandbox Sandbox)
• Search "delf" on MalwareBazaar (Malware Samples)

Frequently Asked Questions

Related Threats (Category: Trojan)

Explore other documented threats in the same operational category:

• Memery
• Sphinx
• Tasker
• Plinch
• Scarcruft
• Collector
• Bump_Rat
• Institution_2004

Machine-readable

Get this profile as JSON: https://malware-families-catalog.systemhelpdesk.com/api/delf.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.