What Are the Security Risks of VoIP for Businesses??

What Are the Main VoIP Security Threats — and How Are They Mitigated?

Toll fraud Toll fraud is the most financially damaging VoIP attack. Criminals gain unauthorised access to your system and make high-volume calls to premium-rate international numbers they control, often running up thousands of pounds in hours. The best defence is a provider that restricts international and premium-rate calls by default, monitors for unusual call patterns in real time, and enforces strong SIP credentials from the outset.

Eavesdropping and call interception Unencrypted VoIP traffic on a poorly secured network can be intercepted and recorded — particularly on shared Wi-Fi or unsegmented networks. Calls should be encrypted end-to-end using SRTP for media and TLS for signalling, and transmitted via secure network infrastructure rather than open internet paths.

SIP scanning and brute-force attacks Automated bots continuously scan for open SIP ports and attempt to authenticate using common credentials. A successful attack lets criminals register rogue extensions or use your system for fraud. IP allowlisting, a Session Border Controller (SBC) at the network edge, and enforced rate limiting are the standard mitigations.

Denial of service attacks Flooding a VoIP system with junk traffic to take phone lines offline is a recognised threat, sometimes used as a distraction during a secondary intrusion. Redundant infrastructure across multiple data centres removes the single point of failure that makes these attacks effective. For wider continuity in any outage scenario, see our guide on keeping VoIP running during a power cut.



Vishing (voice phishing) VoIP makes caller ID spoofing cheap and easy. Attackers impersonate trusted numbers — a bank, an IT provider or HMRC — to manipulate staff into sharing credentials or authorising payments. No technical fix fully addresses this one. Staff training is the primary defence: verify identities through a secondary channel before acting on any unexpected call, and never authorise payments or system access based on a phone call alone. Call recording creates an auditable trail that is invaluable if a dispute arises.

How Does VoIP Stay Compliant With GDPR and PCI DSS?

If your business handles personal data or card payments over the phone, your VoIP system must meet the relevant regulatory standards. Non-compliant call recording, insecure data storage and unencrypted transmission can all result in significant fines. Look for a provider that is UK GDPR compliant, PCI DSS certified and ICO registered, and can evidence it.