Account Takeover Fraud: Detection and Measures for Prevention

What is an Account Takeover (ATO) and How Does it Work?

An Account Takeover (ATO) is a type of cyberattack in which a malicious actor gains unauthorized access to a legitimate user’s online account, such as an email, banking, e-commerce, or gaming profile, and assumes control of it. Once inside, attackers can steal sensitive data, make unauthorized transactions, exploit saved payment details, or use the compromised financial account for further fraudulent activity.

Here’s how it works:

• Credential Stuffing. Attackers use leaked usernames and passwords from personal data breaches to automate login attempts across multiple sites, taking advantage of password reuse.
• Phishing attempts. Victims are tricked into revealing their login credentials via fake emails, websites, or messages that mimic trusted brands or institutions.
• Brute Force Attacks. Automated bot attacks try thousands of password combinations or social security numbers until they crack the correct one, especially effective against weak or reused passwords.
• Man-in-the-Middle Attacks. In insecure networks (like public Wi-Fi), attackers intercept stolen credentials during transmission.

What is an Example of Account Takeover?

A notable example of an Account Takeover occurred in July 2020, when multiple high-profile Twitter account details were compromised to promote a cryptocurrency scam. The attackers employed social engineering techniques to gain unauthorized access to Twitter’s internal administrative tools, enabling them to reset customer account passwords and post fraudulent tweets.

These tweets promised to double any Bitcoin sent to a specific address, leading to over 320 transactions and significant financial losses. The breach affected at least 130 accounts, including those of prominent individuals and companies.

This incident highlights the importance of implementing robust security measures, including multi-factor authentication and security awareness training on phishing and social engineering tactics, to prevent unauthorized access to sensitive systems.

What are the Methods for Executing an Account Takeover Fraud?

Cybercriminals assess various entry points when attempting to gain unauthorized access to an account. Once they have access to it, the credentials can be used to make fraudulent transactions, exfiltrate personal information of the victim’s account, or even penetrate a company’s infrastructure for financial gain.

Account takeover fraud can occur in a variety of ways, including:

1. Phishing

Phishing is still one of the most effective and scalable ATO attempts. In these attacks, victims receive deceptive emails, texts, or voicemails that appear to come from trusted sources, such as banks, service providers, or internal IT teams.

The link inside the message leads to a spoofed website that looks legitimate from a financial institution. When the victim enters their login information, they’re handed over directly to the attacker.

Group-IB’s Business Email Protection combats phishing attacks by automatically detecting and blocking phishing emails, even retroactively, thanks to patented retroactive analysis technology. It also continuously monitors your organization’s email environment to identify new social engineering attempts as they emerge.

2. Malware

Malware designed to harvest credentials can be quietly installed on a device via:

• Malicious attachments
• Infected software downloads
• Drive-by browser exploits

Once inside, malware like infostealers, keyloggers, or banking trojans silently siphon login data, credit card details, and session tokens.

Group-IB’s Fraud Protection can detect and block malware-driven activity patterns before they result in compromised sessions. You can read more in our dedicated blog on banking malware.

3. Data Breaches

When companies experience data breaches, user credentials are often dumped or sold on the dark web, sometimes months before victims become aware. These credentials are then used to commit ATO attacks at scale.

Group-IB Threat Intelligence provides real-time alerts about stolen or leaked credentials associated with your domains or client base. This helps businesses take pre-emptive action before attackers do.

4. Brute-Force Attacks

This method involves bombarding login portals with countless password combinations, especially common passwords, keyboard patterns (like 123456 or qwerty), or variants of leaked credentials. Automated tools make this process fast and highly scalable.

Fraud Protection includes user behavior based detection and bot mitigation that flags unusual login attempts, such as repeated password tries or high-velocity account access attempts to thwart brute-force attacks.

5. Credential Stuffing (Breach Replay)

Attackers know that people reuse passwords. When credentials are leaked in one data breach, they’re tested across dozens (or hundreds) of other services, a tactic known as credential stuffing. It’s low effort, high reward, and very hard to detect without behavioral baselining or user experience.

Group-IB’s layered defense strategy helps organizations identify patterns consistent with credential stuffing attempts, such as login attempts from known compromised accounts or rapid-fire access requests from new IP addresses or devices.

What are the Red Flags of Potential Account Takeover?

Below are the most common red flags that indicate an account may have been compromised:

• Logins from unusual locations, especially countries or regions the user hasn’t accessed from before.
• Multiple failed login attempts, often followed by a successful one, are classic in brute-force or credential stuffing attacks.
• Access at strange hours, inconsistent with the user’s normal user activity window.
• Use of anonymizing tools, like VPNs or Tor, to mask location.
• Email or phone number changes, which attackers often do to cut off account recovery.
• Disabling or modifying two-factor authentication (2FA).
• Updates to password recovery methods or secret questions immediately after login.
• Unusually high-value transactions, withdrawals, or rapid shopping cart checkouts.
• Attempts to transfer loyalty points, rewards, or gift cards.
• Bulk actions like mass downloads, API calls, or linking new external services.
• Repeated, identical actions within milliseconds (e.g., form submissions, page hits).
• Access patterns that skip pages or show unnatural navigation flow.
• Lack of typical human signals like mouse movement or scrolling, etc.
• Logins from devices never seen before, especially when no new-device warning was triggered.
• Known device used from an unfamiliar IP address or browser version.
• Discrepancies between session fingerprint and past behavioral patterns.
• Users report being locked out or noticing unauthorized activity.
• Multiple accounts tied to the same email address, IP, or device fingerprint.
• A spike in password reset requests from real customers who never made the attempt.

Prevent Account Takeover Fraud With Group-IB

In 2021 alone, ATO losses were estimated at $26 billion, but the reputational damage doesn’t stop at dollars. Victims often face anxiety, broken trust, and lasting concerns about data security. For businesses, one breach from bad actors can erode years of brand equity.

As attackers continue to refine their techniques from breach replay to bot-assisted credential stuffing, traditional fraud systems simply can’t keep up.

That’s where Group-IB’s Fraud Protection leads.

Our platform is designed to detect and block account takeover attempts in real-time, utilizing layered risk assessments that extend beyond transactional checks. Here’s how we help stop ATO fraud before it causes harm:

• Behavioral and cross-channel analytics to detect suspicious activity, potential threats, velocity anomalies, and hijacking patterns.
• Passive biometrics and device fingerprinting to flag users logging in across multiple devices or locations.
• Threat Intelligence integration to instantly recognize known malicious IPs, device IDs, and malicious activity.
• Machine learning–powered risk scoring to stop emerging cyber threats and form of identity theft that legacy systems can’t catch yet.
• Global ID is a unique, anonymous identifier that tracks behavioral consistency across multiple sessions and applications, helping to expose fraud rings and repeat offenders.

Group-IB’s approach is proactive, precise, and built for scale, trusted by cybersecurity teams that know every login with sensitive information matters.

Want to see how Group-IB Fraud Protection defends against account takeover attacks in real environments? Let’s talk. We’ll walk you through a live demo or use case tailored to your platform.