Sillysharecopy

Overview

Worm:Win32/Sillysharecopy is a heuristic detection name for a rudimentary, heavily repackaged class of computer worms that propagate primarily by copying themselves to removable drives (USB flash drives) and open network shares. Unlike sophisticated exploits that use vulnerabilities like EternalBlue, Sillysharecopy relies on simplistic file copying and the abuse of Windows AutoRun features or tricking users into clicking on disguised executables to spread.

Understanding Simplistic Network Worms
To an end-user, an infection might not be immediately obvious, but they may notice their USB drives suddenly containing hidden files or strangely named folders that are actually executable `.exe` files. For a network administrator, these worms are a persistent nuisance. They don't typically cause massive immediate destruction, but they create a constant low-level spread of malware across the organization, often acting as a vector for secondary payloads.

Execution and Spreading Mechanics
The initial infection often occurs when a user plugs in a compromised USB drive (`T1091`) or opens an infected file from an open network share (`T1021.002`). When the worm executes (`T1204.002`), it establishes persistence, often by modifying Registry Run keys or dropping a copy of itself into the Startup folder (`T1547.001`). The worm then continually scans the system for newly attached removable drives or mapped network shares (`T1046`). When found, it copies its executable to the root of the drive (`T1570`). It frequently hides the legitimate folders on the drive and creates malicious `.exe` files with the same names and folder icons, tricking the next user into executing the worm when they attempt to open their files (`T1036`). It may also drop an `autorun.inf` file to attempt automatic execution on older systems.

Indicators of Compromise & Impact
The impact is persistent infection and the potential for secondary payload delivery. Host-based IoCs include EDR alerts for anomalous processes constantly enumerating attached drives and copying `.exe` or `.vbs` files to the root directories of removable media and network shares. Users will report that their folders on USB drives have 'turned into applications.'

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:

• T1036: Monitor for executable files running from unusual paths or with deceptive names. Use EDR to detect process masquerading.

MITRE D3FEND™ Defensive Countermeasures

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

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_SILLYSHARECOPY_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Sillysharecopy"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "sillysharecopy" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Sillysharecopy (Advanced Threat) Execution & Triage
id: 3b892ace-35c5-5a4c-a481-60881a0d1335
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Sillysharecopy malware family. Detects proxy execution, reflective DLL
  loading, and remote command injection associated with modular enterprise backdoors.
references:
- https://malware-families-catalog.systemhelpdesk.com/families/sillysharecopy
- https://malware-families-catalog.systemhelpdesk.com/defensive/backdoor-rat-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.advanced-threat
- author.ricky-jordan
- source.systemhelpdesk-mfc
- attack.t1021_002
- attack.t1570
- attack.t1091
- attack.t1036
logsource:
  category: process_creation
  product: windows
detection:
  selection_process:
    Image|endswith:
    - \powershell.exe
    - \cmd.exe
    - \rundll32.exe
    - \regsvr32.exe
    CommandLine|contains:
    - DownloadString
    - IEX(
    - '/s /n /u /i:'
    - sc create
    - start-process
  condition: selection_process
falsepositives:
- Legitimate enterprise administrative scripts during approved change windows
- Authorized IT software deployment utilities and backup management agents
level: high

rule MALWARE_WIN_SILLYSHARECOPY_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Sillysharecopy 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 = "sillysharecopy" 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. Isolate the infected endpoint and immediately disable access to critical, open network shares to prevent the worm from copying itself there.
2. Enforce strict Group Policies to disable AutoRun/AutoPlay for all removable media enterprise-wide.
3. Run specialized AV scans designed to unhide the legitimate folders on affected USB drives and remove the malicious executables.
4. Audit file server permissions; users should only have write access to directories strictly necessary for their role to limit the worm's spread.

What to Avoid

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

1. Do not allow the use of unencrypted, unmanaged USB drives in secure environments, as they are a primary vector for these types of worms.
2. Avoid simply formatting the USB drives if they contain critical data; the data is usually just hidden, not destroyed, and can be recovered.

References & External Analysis

• Search "sillysharecopy" on VirusTotal (External Analysis)
• Search "sillysharecopy" on Any.Run (Sandbox Sandbox)
• Search "sillysharecopy" on MalwareBazaar (Malware Samples)

Frequently Asked Questions

Related Threats (Category: Advanced Threat)

Explore other documented threats in the same operational category:

• Uptodown
• Spoofer
• Rpcdcom
• Veriato
• Speedchecker
• Refogkeylogging
• Somoto
• Lightlogger

Machine-readable

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