Account takeover attacks (ATOs) have become an alarmingly common threat in recent years, putting both individuals and organizations at risk. In an ATO, cybercriminals gain unauthorized access to a victim’s online account, whether it be email, banking, or corporate systems, and then exploit that access for fraud, data theft, or other malicious purposes. These attacks are often automated account takeover campaigns at a massive scale, enabled by myriads of stolen login data circulating on the dark web.
The dark web has become a goldmine of leaked credentials, with an estimated 15 billion stolen username-password pairs available and accessible in underground marketplaces.
With passwords available inexpensively or free, hackers have everything they need to launch widespread account breaches without ever cracking a password themselves.
Instead, they simply buy credentials exposed in dark web data leaks and let bots test the logins on various websites.
What Are Account Takeover Attacks?
Account takeover attacks (ATO) are cyberattacks in which malicious actors gain unauthorized control of someone else’s online account. Essentially, the attacker logs in as the legitimate user, using stolen or hacked credentials, and then has full access to that account. Any type of account can be targeted, from personal email and social media profiles, to online banking and payment accounts, e-commerce accounts, cloud services, and even corporate network logins.
Once inside, the attacker may steal personal data, siphon funds, make fraudulent purchases, or leverage the compromised account to pivot into other systems.
Because the activity comes from a valid account with correct credentials, it often appears legitimate to security systems, enabling the attacker to operate undetected for longer periods.
How do attackers obtain the valid usernames and passwords needed for account takeovers?
Some attackers steal credentials directly through phishing emails or malware via fake login pages or by using keyloggers/info stealers. Others may use brute force methods or password guessing for weak passwords. But, the path of least resistance is to simply buy or collect credentials from past data breaches.
Major breaches expose millions of user passwords, which promptly circulate on underground forums and marketplaces. These stolen login databases or ‘Dark web data leaks’, provide a supply of credential pairs that are ready for attackers to exploit. Dark web data leaks are caches of hacked or leaked data, such as lists of usernames, emails, and passwords, that end up being traded or posted on dark web sites and hacker forums.
The Dark Web: Breeding Ground for Stolen Credentials
The dark web is notoriously known for enabling illegal activities under the cover of encryption and anonymity. One of it’s thriving economies is the trade in stolen data, including login credentials and personal information. When a data breach occurs, the stolen user database often finds its way onto dark web forums within days or even hours.
Dark web marketplaces function like eBay for hackers, offering breached databases, malware, counterfeit documents, and more. These leaked corporate credentials could easily enable attackers to impersonate employees and infiltrate enterprise systems. The dark web makes these data leaks available at scale, in “combo lists” and at low cost.
By monitoring chatter and sales on these underground sites, security teams often see early warning signs of emerging threats. For example, if a company’s user database is being offered for sale on a hacker forum, it is inevitable that their credentials will soon be used in credential stuffing attacks against the company or other services.
This is why dark web monitoring has become a critical practice for organizations. It can keep an eye on the dark web for domain or email addresses and can alert if associated users’ data has been compromised. This will in turn prompt password resets or other defenses before attackers can take advantage.
Automated Account Takeover VS Credential Stuffing
With caches of stolen credentials from the dark web, attackers automate testing each username and password. Automated account takeover refers to orchestrating ATO attacks at scale using bots, scripts, or other software tools to do the heavy lifting.
The most common form of automated ATO is a credential stuffing attack where cybercriminals take a large list of known username/password pairs, typically from a data leak, and use automated software (bots) to try the stolen logins across many different websites- until something works. Essentially, they “stuff” the credentials into login forms on target sites enmasse, hoping that some users have reused the same password.
Credential stuffing is attractive to attackers because it’s cheap, easy, and scalable. Fraudsters simply feed their list of stolen logins into an automated tool, configure some proxies to avoid IP blocking, choose a target website, and let the bot run. The tool will consistently attempt logins for each credential combo, often cycling through thousands or millions of attempts. Any successful logins are recorded for the attacker.
Hackers can test thousands of accounts in minutes, far more than any human could attempt on their own using this method. They also leverage readily available botnets and cracking tools to maximize the efficiency of credential stuffing.
Defending Against Automated ATO Attacks
Dark web data leaks are a major driver of automated account takeover (ATO) attacks. To protect your organization:
- Invest in dark web monitoring tools to scan underground forums and marketplaces for exposed company data, enabling early detection and rapid response. Open source tools are cost effective, while more expensive tools provide better data quality and are more reliable.
- Use automated threat intelligence platforms to continuously watch for stolen credentials linked to your domains.
- Reduce password reuse by enforcing strong, unique passwords with a password manager, setting complexity requirements, educating users, and banning commonly used or previously breached passwords. Some services can check new passwords against leaked databases to prevent compromised credentials.
- Implement multi-factor authentication (MFA) as a critical defense. Even if a password is compromised, a second authentication factor—such as a one-time code or biometric check—can stop most automated attacks without burdening legitimate users.
Discover how Lunar’s proactive monitoring and layered defenses can keep your organization one step ahead of automated threats. Speak to one of our cyber experts to see how Lunar can elevate your security posture.
