Seznam

Overview

Executive Summary

Infection Vector and Technical Capabilities

• Homepage and Search Engine Modification: It aggressively alters the default homepage, new tab page, and default search engine in Chrome, Firefox, and Edge, hardcoding them to redirect to specific affiliate URLs associated with Seznam.
• Extension Installation: It often installs a browser extension to ensure persistence. If the user attempts to manually change their search engine back to Google or Bing, the extension instantly reverts the settings upon the next browser launch.
• Registry Locking: Advanced variants modify Windows Registry keys (or utilize Group Policy Objects) to lock the browser settings, preventing non-administrative users from making changes to their browser preferences.

Threat Assessment

Incident Response and Remediation

• Manual Uninstallation: IT staff should first check the Windows "Add/Remove Programs" list for any recently installed suspicious toolbars or "Search Protect" applications and uninstall them.
• Anti-Malware Scan: Run a comprehensive scan using an enterprise anti-malware solution specifically configured to detect and remove PUPs and Adware registry keys.
• Browser Factory Reset: To completely eradicate the hijacking components and persistent extensions, all installed web browsers must undergo a full factory reset to purge the malicious settings.

Known aliases

Threat reports may refer to this family under multiple names:

• Adware.Seznam
• BrowserHijacker.Seznam
• PUP.SeznamToolbar

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:

• T1105: Implement network intrusion detection systems (NIDS) and host-based firewalls to block unauthorized inbound or outbound file transfers.
• T1185: Enforce strong MFA and use browser isolation or hardened browsers for sensitive financial or administrative portals to defeat session hijacking.

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_SEZNAM_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Seznam"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "seznam" ascii wide nocase
        $s2 = "adware.seznam" ascii wide nocase
        $s3 = "browserhijacker.seznam" ascii wide nocase
        $s4 = "pup.seznamtoolbar" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Seznam (Trojan) Execution & Triage
id: c6d6a96b-17f7-52bc-875d-8cd0ce53a628
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Seznam 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/seznam
- 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.t1185
- attack.t1562_001
- attack.t1055
- attack.t1547_001
- attack.t1105
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_SEZNAM_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Seznam 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 = "seznam" 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 Seznam from retrieving secondary stage payloads.
2. Capture process memory triage to detect and terminate malicious threads injected by Seznam 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 Seznam 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 Seznam 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 Seznam 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 Seznam 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

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

Frequently Asked Questions

Related Threats (Category: Trojan)

Explore other documented threats in the same operational category:

• Moonpie
• Institution_2004
• Mansabo
• Regsup
• Hack_A_Tack
• Filerepmalware
• Yoddos
• Spamer

Machine-readable

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