Lozer

Category: ransomware · Aliases: Trojan.Lozer, Backdoor.Lozer, Win32/Lozer · Sample count (EMBER 2018): 1 · Enrichment: insufficient_information · Updated: 2026-07-01T16:35:09Z

Category: RansomwareActor: Unknown / CybercriminalIndustry: Global / OpportunisticMotivation: Opportunistic

Overview

Executive Summary

Lozer is a malicious Trojan designed to covertly infiltrate Windows systems, establish deep persistence, and act as a reliable backdoor for remote threat actors. Frequently distributed in targeted spear-phishing campaigns, Lozer is often the primary initial access mechanism used to facilitate the deployment of secondary, high-impact malware payloads such as ransomware or enterprise info-stealers.

Infection Vector and Technical Capabilities

Lozer is predominantly distributed through socially engineered spam campaigns containing malicious attachments (often weaponized PDFs or Office documents utilizing macro exploits) or via compromised software installers downloaded from untrustworthy web portals. Upon successful execution, Lozer operates with a focus on stealth and payload delivery:

System Reconnaissance: The trojan immediately collects detailed system information, including the OS version, installed software, Active Directory domain membership, and active antivirus solutions. This fingerprint is transmitted to a command-and-control (C2) server.
Persistence: Lozer ensures it survives system reboots by modifying the Windows Registry (e.g., adding entries to the `Run` or `RunOnce` keys) or by creating hidden Scheduled Tasks that execute the malware payload under high privileges.
Command Execution: Acting as a backdoor, Lozer provides the attacker with a remote shell, allowing them to execute arbitrary system commands, manipulate the file system, and silently download and deploy secondary malware.

Threat Assessment

A Lozer infection represents a critical breach of the endpoint perimeter. Because it provides remote attackers with interactive access and the ability to execute arbitrary code, a single compromised machine can rapidly be utilized to pivot laterally and compromise the entire corporate network.

Remediation and Eradication

Endpoint Detection and Response (EDR): Configure EDR solutions to monitor for anomalous registry modifications and unauthorized outbound network connections to unknown IP addresses.
Network Isolation and Sweeps: Immediately isolate the infected endpoint from the LAN. Conduct a thorough forensic sweep to identify not only the Lozer executable but also any secondary payloads it may have successfully deployed.
Credential Reset: Because Lozer provides an interactive backdoor, all user credentials and active session tokens associated with the compromised endpoint must be treated as compromised and immediately reset.

Known aliases

Threat reports may refer to this family under multiple names:

MITRE ATT&CK Techniques

This family has been observed using the following ATT&CK techniques: T1105 T1547.001 T1059

Tactical Mitigations

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

T1059: Restrict execution of scripting languages such as PowerShell, VBScript, or Python to authorized administrators. Enforce Script Block Logging.
T1105: Implement network intrusion detection systems (NIDS) and host-based firewalls to block unauthorized inbound or outbound file transfers.

Generated Detections (Boilerplate)

These YARA and Sigma rules are auto-generated based on the family name and aliases. They must be heavily tuned before deployment in a production environment.

YARA Rule

rule MALWARE_WIN_LOZER {
    meta:
        description = "Detects Lozer (ransomware)"
        author = "SystemHelpdesk Boilerplate Generator"
        date = "2026-07-06"
    strings:
        $s1 = "lozer" ascii wide nocase
        $s2 = "trojan.lozer" ascii wide nocase
        $s3 = "backdoor.lozer" ascii wide nocase
        $s4 = "win32/lozer" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

Sigma Rule

title: Suspicious Lozer Activity
id: 1001caa5368be3cc623f63a8d0c34c5f
status: experimental
description: Detects generic indicators of the lozer malware family.
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith:
            - '\cmd.exe'
            - '\powershell.exe'
        CommandLine|contains:
            - "*lozer*"
            - "*trojan.lozer*"
            - "*backdoor.lozer*"
            - "*win32/lozer*"
    condition: selection
level: medium

References & External Analysis

Search "lozer" on VirusTotal (External Analysis)

Frequently Asked Questions

How do I remove the Lozer Ransomware from Windows?

Manual removal of Lozer is highly discouraged as it may leave persistence mechanisms intact. We recommend disconnecting the device from the internet and utilizing a professional incident response service or enterprise-grade EDR software to conduct a full forensic sweep.

Is Lozer a virus or a Ransomware?

Lozer is classified as a Ransomware. Unlike traditional viruses that infect files, modern malware like Lozer typically operates as a standalone payload designed to compromise systems, steal data, or deploy secondary stage implants.

What are the main symptoms of a Lozer infection?

Symptoms of Lozer can include unexpected system slowness, unauthorized outbound network traffic to unknown IP addresses, disabled security software, and suspicious background processes running from AppData or Temp directories.

Related Families (Category: ransomware)

Explore other malware families in the same category:

Protect Your Network Against Ransomwares

Want to prevent Lozer and similar threats from compromising your organization? Read our comprehensive defensive guide: Ransomware Protection Guide.

Need help with an active incident? Published by the SystemHelpdesk team.

Machine-readable

Get this profile as JSON: https://jordan123234-malware-families-explorer.static.hf.space/api/lozer.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.