Bancos

Overview

TrojanDownloader:Win32/Bancos is a massive, highly prolific family of banking trojans that historically originated from, and almost exclusively targeted, users in Brazil. It is engineered to monitor browsing activity, detect when a user visits targeted Latin American financial institutions, and steal their banking credentials.

Understanding Bancos
To the victim, a Bancos infection is invisible until their bank account is mysteriously drained. For threat intelligence analysts, Bancos represents a highly localized, deeply entrenched criminal ecosystem. Brazilian threat actors continually iterate on Bancos, making it a cat-and-mouse game for AV vendors. It differs from sophisticated, global trojans (like Zeus) by often relying on simpler, yet highly effective, social engineering and web overlays rather than complex rootkits.

Execution and Evasion Strategies
Bancos is primarily distributed via massive, localized malspam campaigns (phishing emails written in Portuguese, often impersonating Brazilian tax authorities, utilities, or banks). The emails contain links to ZIP files or malicious executables. Upon execution, Bancos establishes persistence (Registry Run keys or scheduled tasks). It continuously monitors the active browser window title or URL (`T1185`). When a targeted Brazilian bank is detected, Bancos springs into action. It often uses localized DNS hijacking (`T1568.002`) or simply drops a fake, full-screen HTML overlay over the legitimate banking site, tricking the user into entering their credentials, CPF (Brazilian taxpayer registry), and two-factor authentication tokens, which are immediately POSTed to the attacker's server.

Indicators of Compromise & Impact
The impact is severe, targeted financial fraud. Incident responders will observe anomalous outbound traffic to C2 servers, often hosted on compromised Brazilian infrastructure. EDR platforms will flag the malware monitoring browser APIs or modifying the local `HOSTS` file to redirect banking URLs. The presence of newly dropped, heavily packed executables in `%AppData%` originating from email clients is a strong IoC.

MITRE ATT&CK Techniques

Observed techniques used by this family, mapped to the MITRE ATT&CK framework:

Tactical Mitigations

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

• T1056.001: Implement Endpoint Detection and Response (EDR) to monitor for suspicious API calls related to keystroke interception. Enforce Multi-Factor Authentication (MFA) to render stolen passwords useless.
• T1185: Enforce strong MFA and use browser isolation or hardened browsers for sensitive financial or administrative portals to defeat session hijacking.
• T1566.001: Scan email attachments for malicious macros, scripts, or suspicious archive files.

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_BANCOS {
    meta:
        description = "Detects Bancos (trojan)"
        author = "SystemHelpdesk Boilerplate Generator"
        date = "2026-07-06"
    strings:
        $s1 = "bancos" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

Sigma Rule

title: Suspicious Bancos Activity
id: 81cfe7bf62c890886b770e5c57fbaa0f
status: experimental
description: Detects generic indicators of the bancos malware family.
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith:
            - '\cmd.exe'
            - '\powershell.exe'
        CommandLine|contains:
            - "*bancos*"
    condition: selection
level: medium

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 halt the active credential harvesting and prevent the attacker from maintaining a live session with the bank.
2. Assume all financial credentials used on the machine are compromised; initiate mandatory password resets and contact relevant banking institutions immediately.
3. Capture a forensic memory image to extract the active Bancos configuration, identifying exactly which financial institutions were targeted.
4. Due to the aggressive credential harvesting, a complete, clean rebuild of the operating system is the most secure remediation.

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 user to type any passwords or access sensitive portals while the machine is infected.
2. Avoid relying solely on basic AV removal, as Bancos frequently updates its persistence mechanisms and drops secondary payloads.

References & External Analysis

• Search "bancos" on VirusTotal (External Analysis)

Frequently Asked Questions

Related Families (Category: trojan)

Explore other malware families in the same category:

• Metel
• Atomicrat
• Iezones
• Hlux
• Driverupdate

Machine-readable

Get this profile as JSON: https://jordanricky1604-ship-it.github.io/malware-families-catalog/api/bancos.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.