VoIP fraud is an increasing risk for businesses, with attacks such as toll fraud, caller ID spoofing, PBX hacking, and call interception exploiting weak security and configuration gaps. Strong authentication, timely updates, secure configurations, network monitoring, employee training, and encryption are essential to preventing unauthorized access and protecting communications.

Companies around the world have already fallen victim to VoIP-related fraud. A single incident can cost an enterprise anywhere from $3,000 to $50,000 - or even more.

VoIP fraud is the unauthorized use of Voice over Internet Protocol systems to place calls, steal data, or execute scams, typically without the victim’s awareness.

Cyber attackers are not only interested in large organizations or direct financial theft. They actively exploit unsecured VoIP systems, using them to carry out scams, make fraudulent calls, or run large-scale attack campaigns. In some cases, attackers don’t even need to generate direct billing costs - your system alone can become a tool in someone else’s fraud operation.

The real question is: is your infrastructure ready to defend against this kind of misuse?

In this article, we take an in-depth look at different types of VoIP scams and how they work, along with essential steps you can take to secure your systems and protect your business from these evolving threats.

Types of VoIP scams

As businesses increasingly adopt VoIP technology, cybercriminals have developed various methods to exploit organizations that do not properly secure their phone systems. Some of the most common types of VoIP scams include:

Toll fraud

Toll fraud is one of the most financially damaging forms of VoIP abuse. It occurs when attackers gain unauthorized access to a company’s VoIP environment - such as a PBX system, SIP trunk, or voicemail platform - and use it to place outbound calls to premium-rate or international numbers under their control. The organization whose system has been compromised is then billed for these calls, often discovering the fraud only after receiving unexpectedly high telecom charges.

How does toll fraud work? Attackers typically begin by scanning internet-facing VoIP systems for exposed SIP services or poorly secured administrative interfaces. Weak passwords, default credentials, and unpatched software are common entry points. Once access is obtained, automated scripts can generate thousands of simultaneous calls, often during nights, weekends, or holidays when monitoring is limited. These calls are placed to premium rate numbers - that charge callers at a higher rate.

The impact of toll fraud can be severe, with organizations facing losses ranging from hundreds to hundreds of thousands of euros or dollars in a matter of hours. A small business in Perth fell victim to this type of fraud after attackers compromised its phone system and placed more than 11,000 unauthorized international calls over a 46-hour period - charges exceeding $120,000.

Caller ID spoofing

Caller ID spoofing is a technique in which attackers deliberately falsify the caller identification information displayed on a recipient’s phone. VoIP systems make caller ID manipulation relatively easy because call signaling protocols, such as SIP, can allow caller identity information to be modified unless additional validation mechanisms are in place.

How does caller ID spoofing work? Scammers begin by impersonating a legitimate phone number, such as one belonging to a bank, government agency, customer service center, or internal corporate extension. Before placing a call, the attacker modifies the caller ID information through a compromised PBX system or insecure SIP trunk to display a trusted number.

This significantly increases the likelihood that the recipient will answer the call and trust the caller's instructions.

Caller ID spoofing is commonly used in vishing (voice phishing) campaigns, technical support scams, debt collection fraud, and business email compromise scenarios that involve voice communication. Reports indicate that, so far in 2026, 70% of organizations have experienced at least one vishing attack.

Spoofed calls may also be used to bypass basic trust mechanisms within organizations. For example, employees may comply with requests if the incoming call appears to originate from senior management or internal IT departments.

PBX system hacking

PBX (Private Branch Exchange) system hacking involves unauthorized access to an organization’s telephone exchange system, particularly IP-based PBX platforms. Modern IP-PBX systems manage internal and external voice communications, voicemail, conferencing, and routing services, making them high-value targets for attackers.

Attackers often target exposed web administration panels, SIP services, remote management interfaces, or voicemail systems protected by weak credentials. Automated scanning tools can identify vulnerable PBX systems connected to the internet, after which attackers attempt brute-force logins, exploit software vulnerabilities, or abuse misconfigured services.

How does PBX system hacking work? Once inside the PBX environment, attackers may create new user accounts, modify call routing rules, enable unauthorized forwarding, record conversations, or use the system for toll fraud. In some cases, attackers maintain persistent access, allowing long-term surveillance or repeated financial abuse.

Because PBX systems often integrate with corporate networks, a compromised PBX may also serve as an entry point for broader network attacks.

One of the largest telecommunications fraud operations on record was the Noor Aziz/Qasmani Global Scheme. In this case, foreign hackers targeted U.S. corporate PBX systems, reprogramming unused phone extensions to enable over $50 million in fraudulent calls. The proceeds were laundered through about 650 bank accounts in ten countries before coordinated international arrests were made.

Eavesdropping and call interception

Eavesdropping is the unauthorized interception of voice communications. In VoIP systems, voice is transmitted as digital packets over IP networks, so if traffic is not properly secured, attackers may capture and reconstruct conversations.

Common methods include packet sniffing on unsecured networks, compromised routers, open Wi-Fi, or malicious access points. More advanced attacks use man-in-the-middle (MITM) techniques, where attackers position themselves between two parties to intercept calls in real time.

How does eavesdropping and call interception work? A VoIP conversation is split into many small packets. Attackers can capture these packets, identify those belonging to a call, reorder them using sequence data, and reconstruct the audio. If SIP credentials are compromised, attackers can perform registration hijacking. They may register their device instead of the legitimate user, redirecting incoming calls to themselves. This allows them to answer, forward, record, or impersonate the user without detection.

This type of attack allows a fraudster not only to intercept communications, but also to actively participate in them without the legitimate user’s knowledge.

A notable example occurred between mid-2024 and early 2025, when major U.S. telecommunications providers - including AT&T, Verizon, Lumen Technologies, and T-Mobile - were targeted by a state-linked threat group known as Salt Typhoon.

The campaign affected sensitive communications across both government and private-sector organizations and is widely regarded as one of the most significant telecommunications breaches in U.S. history.

Essential security practices

To reduce the risk of VoIP fraud and cyberattacks, businesses should prioritize essential security measures.

Strong authentication and access control

Yes, ‘Name123’ is an easy-to-remember password, but it is also very easy for someone else to figure out. Instead, use strong, unique passwords for all VoIP accounts, voicemail systems, and administrative interfaces, and enable multi-factor authentication where possible. Default credentials should always be changed, and remote access should be limited to trusted networks or VPN connections.

Regular updates and secure configurations

Keep VoIP software, firmware, and PBX systems regularly updated to patch known vulnerabilities. Unnecessary services, open ports, and exposed management interfaces should be disabled to reduce the attack surface.

Network monitoring and call restrictions

Monitor call activity in real time and configure alerts for unusual behavior, such as high call volumes, after-hours activity, or unexpected international calls. Restrict access to premium-rate and international dialing unless it is required for business operations, and implement CAPS (Call Attempts Per Second) restrictions and spending limits to control call charges, prevent unauthorized usage, and reduce the risk of toll fraud.

Encryption and network protection

Transport Layer Security (TLS) protects SIP signaling by encrypting call setup and control messages, while Secure Real-time Transport Protocol (SRTP) encrypts the audio stream itself. When properly implemented, these technologies prevent attackers from easily decoding intercepted packets, even if network traffic is captured. Securing wireless networks and separating VoIP devices from the main corporate network can further reduce the risk of interception.

Employee awareness and verification

Train employees to recognize social engineering attempts such as vishing and caller ID spoofing, and to avoid trusting caller identity alone. Sensitive requests, especially involving payments, credentials, or confidential information, should always be verified through an independent communication channel.

Continuous auditing and incident detection

Regularly review system logs, access records, and configuration settings to identify suspicious activity early. Continuous monitoring and routine security audits help detect unauthorized access before it results in financial loss or operational disruption.

Conclusion

Cybercriminals' tactics continue to evolve, and organizations must keep pace by continuously strengthening their systems through regular updates, advanced threat detection, employee training, and strong data protection.

Cybersecurity should be viewed not only as an IT responsibility but as a core part of business strategy and risk management. Companies that prioritize it are better positioned to protect sensitive data, maintain customer trust, and minimize the financial and reputational impact of cyber incidents.

DIDWW maintains automated, round-the-clock quality and abuse monitoring to ensure the integrity and consistently high audio quality of our voice and SMS routes. Our global private network is supported by professional in-house monitoring operating 24/7/365, ensuring reliable and secure communications for our customers worldwide. For enhanced security, SRTP encryption is enabled by default. To learn more about our services, please contact us at sales@didww.com or connect with us via live chat at any time.