Security for Digital Banks: the anatomy of an account takeover response

Why digital banks are the number one target of organized digital crime in Brazil

Brazilian digital banks concentrate, within just a few apps, exactly what financial organized crime desires most: active checking accounts, PIX keys, credit limits, complete registration data, and the ability to move money in real time, 24 hours a day, seven days a week. Unlike a data breach that must be monetized later — sold, cross-referenced, used in third-party fraud — an attack on a digital bank has an immediate financial return. An account taken over today becomes an outbound PIX within minutes. This immediacy of profit is what places the subsector at the top of the priority list for the digital criminal groups operating in the country.

The nature of the product aggravates the risk. A digital bank is, by definition, a financial institution with no physical branch, whose only point of contact with the customer is the digital channel — mobile app, internet banking, partner APIs, and the Open Finance ecosystem. The entire attack surface is exposed on the public internet, accessible from anywhere in the world, and the whole operation depends on software. There is no manager who recognizes the customer, no teller who asks for an ID. Identity is proven by credentials, devices, and authentication factors — precisely the elements the attacker seeks to subvert.

Add to this the competitive pressure around user experience. The digital bank customer expects to open an account in minutes, without friction, and to transact with just a few taps. Every security control that adds friction is seen by the business as a conversion and churn risk. The result is a permanent tension between the product area, which wants to remove barriers, and security, which needs verification points. Resolving this tension is not about choosing a side — it is about designing controls that are invisible to the legitimate customer and impassable to the fraudster. This can only be done with behavioral intelligence and adaptive risk, not blind blocking.

The five threats that bring down digital banks the most

1. PIX fraud and mule account opening

PIX fraud manifests at two ends. On the outbound side, legitimate accounts taken over by attackers dump their balance into mule recipients. On the inbound side, criminals open mule accounts en masse — using third-party data, synthetic documents, or stolen identities — to receive the proceeds of scams run against other institutions and rapidly disperse the money through a web of transfers. The digital bank, because of its fast onboarding, is especially vulnerable to becoming the unwitting 'laundry' of this chain. The defense requires antifraud at onboarding (liveness proof, document validation, device recurrence checks) combined with monitoring of movement patterns that reveal mule behavior.

2. Account takeover via banking malware and SIM swap

Brazilian banking trojans are among the most sophisticated in the world. They install themselves on the customer's device, frequently abusing Android's accessibility services, and operate through overlay (fake screens superimposed on the legitimate app), credential capture, and, in some cases, remote control of the device to initiate transactions from within the victim's trusted device. SIM swap attacks the second factor: the criminal ports the victim's number to a chip under their control and intercepts authentication SMS messages and recovery codes. In both cases, the result is the same — the attacker authenticates as the customer. Detection must migrate from credentials to behavior and device integrity. It is worth remembering that SMS-based MFA, inherited from an earlier era, is precisely the link that SIM swap and malware break: mature banks are moving toward strong phishing-resistant authentication (FIDO2/passkeys, hardware biometrics, device binding) combined with adaptive risk.

3. Credential stuffing, bots, phishing, and API attacks

Billions of leaked email and password pairs circulate freely; attackers test them en masse against the login screen (credential stuffing), while bot farms automate account creation for fraud. In parallel, phishing and social engineering exploit the human link with fake pages, fraudulent SMS and WhatsApp messages, and fake 'security center' agents. Finally, Open Finance has expanded the surface: data and payment initiation flow through APIs, and the classic OWASP API Security vectors — Broken Object Level Authorization (BOLA), weak authentication, excessive data exposure, lack of rate limiting — apply in full. Defending them requires intelligent rate limiting, automation detection, cloned-brand monitoring, hardening, and rigorous schema validation of the APIs.

The defense window: why every minute defines the loss

In an account takeover wave, the attacker's timeline is brutally short. From the moment the credential or device is compromised to the outbound transfer via PIX, only minutes usually pass. The fraudster does not delay because they know the antifraud clock is running. This inverts the traditional security logic, which tolerated hours or days between detection and response. In a digital bank, detection must be in real time and containment nearly immediate.

It is this reality that makes Decripte's containment SLA of up to 1 hour not a marketing number, but an operational requirement. In practice, technical-layer containment — account blocking, freezing of a suspicious transaction, session and token revocation — must be automated and trigger within seconds when the risk pattern crosses the threshold. The 1h SLA covers the coordinated human response to the incident: scope analysis, identification of the other accounts affected by the same campaign, communication, and eradication. Automation wins the minutes; the team wins the war.

How Decripte detects the anomalous pattern before the money leaves

Decripte's 24x7 SOC ingests and correlates, in real time, the telemetry that matters in a digital bank: authentication events (success, failure, new device, new IP, geolocation), device integrity signals, Open Finance and PIX API events, and the transactional flow. The goal is not to look at an isolated event, but to recognize the campaign's pattern. A successful login is not suspicious in itself; a successful login from a new device, in a geolocation incompatible with the customer's recent activity, followed within seconds by the registration of a new PIX key and an attempted high-value transfer to a recipient never seen before, is the classic signature of takeover.

When the same signature appears across dozens of accounts within a short window, the SOC recognizes that it is not an isolated incident but a wave — probably fed by a malware or phishing campaign active at that moment. This recognition of the collective pattern is what allows containment not only of the first detected account, but of all those sharing the campaign's indicators, getting ahead of the frauds that have not yet been executed.

Correlation is what separates noise from signal. On its own, each of these events generates thousands of legitimate occurrences per day. Combined into a coherent temporal sequence, they draw out the attacker's intent. Decripte's SOC runs this correlation continuously, with analysts on duty for triage, escalation, and activation of incident response the instant the pattern is confirmed.

Layered defense: the architecture that sustains a digital bank

No isolated control protects a digital bank. Effective defense is defense in depth — multiple independent layers, so that the failure of one does not compromise the whole. Decripte structures this architecture on five mutually reinforcing layers.

Identity, antifraud, and API

The identity layer applies strong phishing-resistant authentication, device binding, and adaptive risk, which raises the verification requirement in proportion to the operation's risk — a routine login flows without friction, but the registration of a new PIX key followed by a high transfer from a new device triggers additional verification. The behavioral antifraud layer learns the normal behavior of each account and flags deviations, distinguishing the real customer from the attacker who holds valid credentials, both at onboarding (mule accounts, synthetic identities) and in operation (mules, bots). The API hardening layer treats the Open Finance and PIX APIs as first-class citizens: rigorous object-level authorization (mitigating BOLA), strict schema validation, rate limiting, protection against unrestricted resource consumption, and auditable consent management.

Edge and continuous monitoring

The edge layer uses a WAF to filter malicious traffic, DDoS protection to ensure availability (an unavailable bank is, in itself, a regulatory and reputational incident), and bot mitigation to contain credential stuffing and account-creation farms before they reach the application. The continuous monitoring and response layer stitches all the previous ones into unified visibility: the 24x7 SOC, the continuous vulnerability management that keeps the technical surface under control, and the incident response capability that acts when prevention fails. Without this layer, the previous ones are static snapshots of a target that changes every day.

Compliance that becomes control: PCI-DSS, LGPD/ANPD, and Bacen

For a digital bank, compliance is not a documentary exercise — it is the translation of regulatory obligations into verifiable, continuously monitored technical controls. Decripte treats each requirement as a set of auditable controls, not as an annual report that sleeps in a drawer. PCI-DSS applies to any environment that stores, processes, or transmits card data, covering network segmentation, encryption, vulnerability management, access control, monitoring, and regular security testing — including pentesting. Decripte structures the environment, runs the required tests, and keeps the evidence alive, so that compliance is continuous, not an audit snapshot.

The LGPD, enforced by the ANPD, governs the processing of personal data. Customers' financial and registration data are among the most sensitive under the law, and an incident that exposes them can trigger the obligation to notify the ANPD and the data subjects. Decripte helps design the protection, minimization, and processing-record controls and — crucially — the ability to detect and respond to incidents within the deadlines and rigor that the law and the ANPD's understandings expect.

Banco Central has specific regulations on cybersecurity policy and requirements for financial institutions' contracting of data processing and storage services and cloud computing. Decripte's defense architecture and response processes are designed to align with these requirements, helping the bank demonstrate security governance maturity to the regulator. Add to this ISO 27001 and SOC 2 as information security management references that reinforce the confidence of partners and investors.

The continuous cycle: pentesting, vulnerability management, and the engine that learns

A digital bank's attack surface changes with every deploy. New features, new Open Finance integrations, new versions of the mobile app — each change can introduce a vulnerability. That is why security cannot be a one-off event; it must be a continuous cycle that keeps pace with the rhythm of development.

Decripte's vulnerability management keeps the technical surface under constant inventory and prioritization: it identifies what is exposed, classifies it by real risk (not just theoretical severity), and tracks remediation through to closure. Pentesting and the red team exercise complement this, simulating the real adversary — testing the mobile app, external APIs, authentication flows, and antifraud controls with the same creativity as organized crime. What the attacker would do first, Decripte does before, in a controlled environment.

Start with the diagnostic, evolve into the managed service

The first step is to understand the real exposure. Decripte's free Threat Management diagnostic, at decripte.com.br/intelligence-center, maps the bank's visible attack surface — exposed assets, cloned-brand indicators, exposure signals — and delivers an honest snapshot of the risk before it becomes an incident. It is the fastest way to discover what an attacker can already see.

From this diagnostic, the natural evolution is the managed service: 24x7 SOC, incident response with a containment SLA, recurring pentesting, vulnerability management, and the compliance program. Engagement begins at decripte.io/start, and any specific question about your bank's scenario can be handled directly at /contato. The security of a digital bank is not bought like an off-the-shelf product — it is built as a continuous operation, and that is exactly how Decripte delivers it.

Anatomy of a real case: an account takeover wave driven by a banking trojan

How Decripte responds to an incident at a digital bank

Decripte's incident response for digital banks is designed around the extremely short window between compromise and the money leaving. The flow prioritizes stanching the financial bleeding first, investigating afterward, and hardening at the end — always within the containment SLA of up to 1 hour for the technical layer.

1. Real-time detection and triage: the 24x7 SOC correlates login, device, API, and transaction telemetry, recognizes the anomalous pattern (not the isolated event), and confirms whether it is an isolated incident or a coordinated wave.
2. Activation and classification: upon confirming the risk pattern, the analyst on duty opens the incident, classifies the severity, and activates the response team, starting the containment SLA clock.
3. Automated containment of the technical layer: blocking of compromised accounts, freezing of suspicious transfers, and revocation of sessions and tokens within seconds, before the PIX settles.
4. Scope expansion and preventive containment: identification of all accounts sharing the campaign's indicators and extension of containment, including to accounts not yet defrauded, getting ahead of the attacker.
5. Root cause eradication: extraction of malware and phishing campaign indicators, takedown of domains cloning the brand, mapping of mules, and updating of the antifraud and SOC correlation rules.
6. Secure recovery: rehabilitation flow for legitimate accounts with reinforced verification, credential rotation, reassessment of trusted devices, and reversal of transfers blocked in time.
7. Meeting the regulatory obligation: support for incident documentation and the communications required by LGPD/ANPD and Bacen regulations, within the expected deadlines and rigor.
8. Post-mortem and hardening: lessons become permanent controls — new rules, authentication and adaptive risk adjustments, and the scope of the next pentest — closing the continuous learning cycle.

How Decripte structures the security of a digital bank

Before and beyond the incident, Decripte builds a defense-in-depth architecture sustained by continuous monitoring. There are five mutually reinforcing pillars, so that the failure of one does not compromise the whole.

Recommended plans for Digital Banks

Frequently asked questions

Sector terms

Account takeover (ATO)

The takeover of a legitimate account by an attacker who obtains its credentials or controls the victim's device — typically via banking trojan, SIM swap, or phishing — authenticating as the real customer to carry out fraudulent transactions.

SIM swap

Fraud in which the criminal transfers (ports) the victim's phone number to a chip under their control, then intercepting authentication SMS messages and recovery codes, which breaks the text-message-based second factor.

Credential stuffing

An automated attack that tests, en masse, email and password pairs leaked from other services against the bank's login screen, exploiting users' password reuse.

BOLA (Broken Object Level Authorization)

An object-level authorization flaw in which an API allows one user to access another's data or resources by manipulating identifiers. It is one of the main OWASP API Security categories and a central risk in Open Finance.

Open Finance

An ecosystem for sharing data and initiating payments between financial institutions and authorized third parties, via APIs. It expands the range of services, but also the attack surface, requiring rigorous hardening of the integrations.

Defense in depth

A security strategy based on multiple independent control layers — identity, antifraud, API, edge, and monitoring — so that the failure of one layer does not compromise the system as a whole.