Account Takeover (ATO) Prevention

An account takeover (ATO) is a form of cyberattack where malicious actors use stolen credentials, weaknesses in account security, or compromised authentication to log into accounts. Depending on the type of account they gain access to, the attackers may then steal financial information, exfiltrate company data, or abuse the account’s permission level to disable company-wide security protections.

What Are Account Takeover (ATO) Attacks?

Account takeover attacks typically originate from malicious groups buying stolen usernames and passwords in bulk. If login credentials are involved in a breach, then their details are typically published on the dark web for attackers to purchase or use. By using bots to test these credentials en masse on connected websites, hackers hope to gain entry to valuable accounts.

Most of the time, attackers focus on email ATO, as email accounts often act as a central hub for all other accounts. For example, if an attacker has access to an email account, they could then reset a password on a different site, using the email account as the primary recovery and verification channel.

Especially in the case of email, one compromised account can lead to a wider breach, as attackers can move laterally, impersonate verified individuals, and distribute phishing messages internally from a trusted source. Additionally, as malicious actors aren’t always forcefully breaching an account (rather, they just use the correct username and password combination), there are fewer indicators of compromise when compared to a traditional intrusion-based attack.

How ATO Attacks Work

Account takeovers aim to fly under the radar as much as possible, meaning that the attack vectors malicious actors use tend to be less invasive than most cyberattackers.

The main ATO strategies that groups will use include the following:

Stolen Credentials: Stolen credentials are an extremely common method that malicious actors will use to break into accounts. If usernames and passwords leak in a data breach, they become accessible to groups that can then use them on a variety of accounts to try and find one that’s useful to them. While multi-factor authentication helps protect against many credential-based login attempts, if employees fail to set this up, they’re leaving the door open to ATOs.
Password Spraying: Password spraying is a strategy where malicious groups use bots to enter common passwords on thousands of accounts concurrently. Instead of focusing on just one account, which would trigger a lockout or an alert, they instead try one or two passwords per day for long periods.
Brute-Force Attacks: Brute-force attacks are a more direct form of password attack, focusing on one account and trying as many passwords as possible with a bot. While this is a potential attack vector for an ATO, it’s less common, as many modern password systems will lock accounts after a few unsuccessful login attempts.
Phishing Attacks: According to the Check Point State of Cybersecurity 2025 Report, phishing attacks are the #1 most common initial access vector. Accounts compromised through phishing often spiral into further ATO incidents, as a trusted account can deliver malware or more easily move laterally through a system.
MITM Attacks: Man-in-the-Middle attacks hijack connections as they pass between endpoint devices and a service. By using an MITM attack vector to capture an authentication token, for example, attackers can then use that token to bypass the need for passwords entirely. MITMs are a concern even for accounts protected by MFA, as they can bypass this mechanism entirely and give attackers direct access to the account.
Malware Attacks: There are several forms of malware that can lead to an account takeover. Traditionally, keyloggers that would record username and password data would allow attackers to silently capture the information they needed for an ATO. More recently, specialized malware that targets browsers and authentication cookies helps attackers to bypass the need for credentials and hack active accounts without triggering alarms.

Consequences of a Successful ATO Attack

Part of the reason that ATO attacks are so dangerous is that many of the attack vectors above, bar brute force attacks, are almost completely silent. Account takeover attacks often use valid credentials, malicious actors simply logging into company or individual accounts just like the real owner of the account would. Without triggering any major security alarms, traditional security controls may not notice an unauthorized presence in their system before they begin a more devastating attack.

The specific account that actors are able to take over also directly impacts how severe the consequences are. For example, if a group is able to launch a successful ATO on an account with admin privileges, then that high level of access and permissions trust is inherited by the attackers. They could then disable security controls, mass distribute malware across the company, or access sensitive data and exfiltrate it as quickly as possible.

Beyond these potential consequences, another impact of a successful ATO is reputational damage. If it becomes public knowledge that your company was responsible for customer data being exfiltrated, then long-term customers may lose their faith in your ability to protect their data. Although more difficult to quantify, this can lead to revenue damages across the board.

How to Prevent Account Takeover (ATO) Attacks

Although ATOs can fly under the radar, there are several strategies and tools that businesses can turn to in order to mitigate them. Because ATOs often rely on legitimate credentials, organizations need to focus on reducing credential exposure, identifying abnormal account behavior, and limiting the scope attackers have once inside a system.

Here are some security best practices to prevent ATOs:

Enforce Strong Passwords: If a user has a strong password, they instantly eliminate the opportunity for attackers to correctly guess their account login just by using default or common passwords. Organizations should enforce password standards that include special characters, long password lengths, and the need to change a password every few months.
Enable Multi-Factor Authentication: MFA is a central strategy in reducing ATOs, as it can completely stop any breaches based on simply using the right username and password. Needing multiple forms of authentication will add a much-needed extra layer of protection to business accounts. It should be enabled by default in your company, with every new account needing to set up an alternative device for authentication.
Isolate Accounts Through Sandboxing: Sandboxing accounts in this context refers to enforcing permission restrictions and network segmentation controls on accounts. By limiting the scope of access an account has in a business to only the essential files or archives it needs to perform its function, then a hacked account has a significantly shortened scope. Sandboxing helps to prevent lateral movement and reduce the severity of ATOs.
Educate Employees on Security Awareness: Teaching employees about common threats and how to protect their accounts will decrease the number of human-error-based breaches in your business. Even just educating about how to spot phishing or false MFA emails can go a long way to stopping account takeovers.
Deploy WAFs: Web Application Firewalls allow businesses to block requests from known attackers, identify bot connections and disable them, and prevent credential stuffing or password spray attacks.
Protect APIs: Businesses have to contend with enormous attack surfaces, especially when considering how many different APIs are active in a company network. Securing every single API with authentication controls and behavioral monitoring will prevent them from becoming an entry point for further ATO attacks.
Adopt an Advanced Email Security Solution: Modern email security solutions will couple traditional threat monitoring with behavioral analysis and machine learning to better detect when an unauthorized presence is using an account. By stopping ATOs before attackers are able to interact with your company systems, you can dramatically reduce how effective they are.

Protect Enterprise Email & Collaboration with Check Point

While account takeover attacks may come as a surprise to the individual, the attack itself creates a pattern of behavioral anomalies and strange activity that cybersecurity tools can pick up on. Check Point Harmony & Email Collaboration identifies the signals of a compromised account as early as possible, using ML algorithms to flag and isolate suspicious user behavior before damage occurs.

Harmony uses advanced behavioral analysis and monitors over 100 event indicators across email and collaboration platforms, like suspicious mailbox configurations, uncommon mass internal email activity, password resets, and changes to MFA settings. Aligning these signals with other potential indicators of a breach allows Harmony to lock accounts that may have been compromised before attackers can take further action.

Account takeover protection is delivered as a part of Harmony’s unified email and collaboration security platform, extending to AI-driven phishing prevention, malware protection, and automated threat response workflows. By centralizing visibility, filtering out false-positive alerts, and indicating to security engineers the best remediation pathway, security teams can put their trust in Harmony to effectively contain ATOs.

Build a stronger security posture for your email and collaboration platforms by requesting a demo today.