Whenu

Overview

Executive Summary

Distribution and Technical Behavior

• Contextual Ad Delivery: The core component of WhenU (SaveNow) actively monitored the URLs a user visited and the search terms they entered into search engines. If a user searched for "flights to London," WhenU would instantly generate a pop-up advertisement for a competing travel agency.
• Local Database and Updates: Rather than querying a server for every ad, WhenU downloaded a massive, encrypted database of keywords and corresponding affiliate links to the local hard drive. This allowed it to serve ads instantly without generating massive amounts of network traffic, hiding its operations from early firewalls.
• Deceptive EULA: WhenU was notorious for its End User License Agreement (EULA), which buried the details of its tracking and ad-serving behaviors deep within pages of legal jargon, allowing the company to claim users had "consented" to the adware.

Risk Assessment

Mitigation and Removal Strategies

• Endpoint Scanning: Modern enterprise-grade anti-malware solutions easily detect and remove WhenU and its associated components. A full system scan will identify the executables and the local ad databases.
• Application Control: The primary defense against adware like WhenU is enforcing strict application whitelisting policies, preventing standard users from executing unapproved software installers (especially P2P clients) that serve as the distribution vector.
• Legacy Systems: While WhenU is largely extinct on modern OS architectures, legacy systems (Windows XP/7) used in specific OT environments should be scanned to ensure these classic adware families are not silently consuming resources.

Known aliases

Threat reports may refer to this family under multiple names:

• Adware.WhenU
• PUP.SaveNow
• Adware.WhenUSave

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:

• T1566.002: Inspect email links for known malicious domains and use link-rewriting services for time-of-click analysis.

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_WHENU_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Whenu"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "whenu" ascii wide nocase
        $s2 = "adware.whenu" ascii wide nocase
        $s3 = "pup.savenow" ascii wide nocase
        $s4 = "adware.whenusave" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Whenu (Advanced Threat) Execution & Triage
id: 4d790d67-8566-5de6-8b4c-e3b418c61f99
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Whenu 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/whenu
- 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.t1112
- attack.t1566_002
- attack.t1176
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_WHENU_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Whenu 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 = "whenu" 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. Enforce forensic network isolation on all suspected endpoints while maintaining an out-of-band telemetry conduit to capture live Whenu adversary activity.
2. Perform full memory dumps across identified staging nodes to extract memory-only implants, kernel rootkit hooks, and decrypted Whenu C2 infrastructure IP/domain lists.
3. Review Active Directory domain controller authentication logs for anomalous Kerberos ticket requests (Pass-the-Ticket, Golden Ticket) and unauthorized DCSync operations associated with Whenu.
4. Block all confirmed C2 domains, dynamic DNS endpoints, and proxy IP addresses across perimeter firewalls, proxies, and DNS security gateways.
5. Conduct an enterprise-wide sweep across surrounding subnets for secondary webshells, WMI event subscriptions, or remote execution tooling left behind by Whenu operators.

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

Frequently Asked Questions

Related Threats (Category: Advanced Threat)

Explore other documented threats in the same operational category:

• Syncopate
• Fakerean
• Kingsoft
• Xunleihd
• Vonteera
• Stufffull
• Joke
• Filerepmetagen

Machine-readable

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