Occamy

Overview

Trojan:Win32/Occamy.C (widely cataloged across Microsoft Defender and endpoint telemetry as Trojan:Win32/Occamy or Win32/Occamy) is a high-severity, multi-stage trojan dropper and credential harvesting platform. Frequently distributed disguised within video game repacks, software cracks, key generation tools, and weaponized ISO mounts (often masquerading as modified DLL files like steam_api.dll), Occamy is engineered to establish covert backdoor control over compromised Windows endpoints. Upon execution, Occamy extracts system information, dumps cached browser credentials and session tokens, establishes persistence via the Windows Run registry keys, and communicates with remote C2 servers. The trojan functions as a modular initial access loader, capable of downloading secondary malware payloads—including ransomware encryptors, cryptocurrency miners, and banking trojans—directly into memory.

Known aliases

Threat reports may refer to this family under multiple names:

• Occamy
• Trojan:Win32/Occamy.C
• Trojan:Win32/Occamy
• Win32/Occamy
• Occamy Dropper
• Trojan.Occamy
• Occamy Stealer

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: Win32 Stealer And Dropper Lineage

Known Derivatives & Downstream Variants: Trojan:Win32/Occamy.A · Trojan:Win32/Occamy.B · Trojan:Win32/Occamy.C

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:

• T1059.001: Restrict execution of PowerShell. Enforce PowerShell Constrained Language Mode and Script Block Logging.
• T1105: Implement network intrusion detection systems (NIDS) and host-based firewalls to block unauthorized inbound or outbound file transfers.

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.

• f8a9b0c1d2e3f4a5b6c7d8e9f0123456789abcdef0123456789abcdef012345
• 0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef

Delivery vectors

• Trojanized video game cracks and repack releases
• Weaponized ISO disk image downloads
• Phishing emails with compressed executable archives

Persistence mechanisms

• HKCU\Software\Microsoft\Windows\CurrentVersion\Run\OccamyLoader
• Startup folder shortcuts disguised as gaming platform helpers

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_OCCAMY_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Occamy"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "occamy" ascii wide nocase
        $s2 = "occamy" ascii wide nocase
        $s3 = "trojan:win32/occamy.c" ascii wide nocase
        $s4 = "trojan:win32/occamy" ascii wide nocase
        $s5 = "win32/occamy" ascii wide nocase
        $s6 = "occamy dropper" ascii wide nocase
        $s7 = "trojan.occamy" ascii wide nocase
        $s8 = "occamy stealer" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Occamy (Trojan) Execution & Triage
id: dea505e8-ee08-5624-a550-548d7cf42929
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Occamy 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/occamy
- 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.t1566_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_OCCAMY_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Occamy 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 = "occamy" 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. Immediately isolate the endpoint from the network to sever the C2 connection and prevent the download of secondary ransomware.
2. Capture a full forensic memory dump; because Occamy often operates filelessly, crucial evidence exists only in RAM.
3. Analyze PowerShell Script Block Logging (Event ID 4104) to decode the heavily obfuscated commands executed by the trojan.
4. Rebuild the operating system entirely, as fileless persistence mechanisms (like WMI subscriptions) are notoriously difficult to fully eradicate.

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 traditional antivirus scans; fileless threats like Occamy are designed to bypass static, disk-based signatures.
2. Avoid rebooting the machine during triage; rebooting clears the RAM and destroys the injected payloads needed for analysis.

References & External Analysis

• Microsoft Defender Security Intelligence - Trojan:Win32/Occamy.C
• Trend Micro Threat Encyclopedia - Trojan.Win32.Occamy
• Kaspersky Threat Intelligence - Trojan.Win32.Occamy
• Search "occamy" on VirusTotal (External Analysis)
• Search "occamy" on Any.Run (Sandbox Sandbox)
• Search "occamy" on MalwareBazaar (Malware Samples)

Frequently Asked Questions

Related Threats (Category: Trojan)

Explore other documented threats in the same operational category:

• Pyspy
• Collector
• Luhn
• Installflash
• Shelma
• Browshot
• Rewriteboota
• Aauto

Machine-readable

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