For most businesses, email remains the centre of daily operations. Quotes are approved, invoices are processed, contracts are shared, and important decisions are made through inboxes every day. That reliance on email is exactly why cybercriminals continue to target it.
One of the most damaging threats businesses face today is the account takeover attack. Unlike traditional phishing scams that rely on obviously suspicious messages, account takeover attacks involve criminals gaining access to a legitimate mailbox and using it to carry out fraud, steal information, or gain access to other business systems.
Because the emails come from a genuine account and often appear in existing conversations, they can be extremely difficult to detect.
How Account Takeovers Happen
Most account takeovers are not the result of sophisticated hacking techniques. Instead, attackers usually exploit everyday behaviours and security gaps.
Stolen credentials are one of the most common entry points. If an employee reuses passwords across multiple services, credentials exposed in a separate data breach can potentially provide access to their business email account.
Phishing also continues to be highly effective. Attackers create convincing sign-in pages, document-sharing notifications, or urgent requests that encourage users to enter their login details without realising they are handing them over to criminals.
Even organisations that use strong password policies can be vulnerable if multi-factor authentication (MFA) is not consistently enforced. In some cases, attackers can also hijack active sessions, allowing them to gain access without ever needing a password.
The key point is that account takeovers often begin with a small mistake during a busy working day. A single click can provide an attacker with everything they need.
What Criminals Do Once They Gain Access
When attackers gain access to a mailbox, they rarely act immediately. Instead, they spend time observing.
They read conversations, review contacts, and learn how the business operates. They identify who approves payments, which suppliers are regularly contacted, and what communication styles employees use.
With that knowledge, attackers can send highly convincing messages that blend seamlessly into normal business activity.
Many criminals search inboxes for terms such as invoice, payment, payroll, contract, or bank details. These keywords help them identify opportunities for financial fraud or data theft.
A particularly effective tactic is email thread hijacking. Rather than creating a new message, attackers reply to an existing conversation. The recipient sees a familiar sender, a genuine email history, and a request that appears entirely legitimate.
Attackers may also create mailbox rules that automatically hide or forward emails, helping them remain undetected for longer. In some cases, they use the compromised mailbox to reset passwords and gain access to other business systems.
At that point, what started as a single compromised inbox can quickly become a wider security incident.
Why These Attacks Are Difficult to Identify
Traditional security awareness training often focuses on obvious warning signs such as poor spelling, suspicious links, or unusual email addresses.
Account takeover attacks are different.
The sender address is genuine because the attacker is using a real account. The message often references actual projects, conversations, suppliers, and invoice numbers. There may be no malicious attachments and no suspicious links.
To the recipient, everything appears normal.
Attackers rely on trust, context, and the speed at which modern businesses operate. When people are handling multiple tasks at once, a realistic email request can easily avoid scrutiny.
Warning Signs Your Business Should Not Ignore
While account takeover attacks are designed to be discreet, there are indicators that something may be wrong.
Unexpected login alerts, unfamiliar password reset notifications, or sign-in activity at unusual times should always be investigated.
Unexpected mailbox rules are another major warning sign. Rules that forward messages externally, move emails to unusual folders, or delete messages automatically deserve immediate attention.
Businesses should also be concerned if suppliers or customers report missing emails, unusual requests, or payment changes that nobody internally recognises.
Similarly, unfamiliar emails appearing in Sent Items can indicate that an account is being actively abused.
Small anomalies often provide the first indication of a larger problem, making early investigation critical.
How to Reduce the Risk
No organisation can eliminate cyber risk entirely, but several practical measures can significantly reduce the likelihood and impact of account takeover attacks.
Strong authentication should be enforced across all user accounts, not just senior leadership. Every mailbox can potentially become an entry point for attackers.
Businesses should encourage the use of unique passwords and provide secure password management tools where appropriate.
Payment processes also deserve special attention. Any request to change banking details or payment instructions should be verified using a trusted method outside of email, such as a phone call to a known contact number.
Employee training should move beyond traditional phishing awareness and include real-world examples of thread hijacking, business email compromise, and payment fraud attempts.
Finally, organisations should have a clear incident response process in place. When a compromise is suspected, teams should know exactly how to secure the account, investigate activity, and notify affected stakeholders.
Protecting Your Business Before an Incident Occurs
Account takeover attacks are successful because they exploit something businesses rely on every day: trust. When criminals can operate from a genuine mailbox, traditional warning signs often disappear.
The good news is that a combination of stronger authentication, better visibility, secure payment procedures, and informed employees can dramatically reduce the risk.
By taking proactive steps today, businesses can make it significantly harder for attackers to gain access, remain undetected, and turn a compromised mailbox into a costly incident.