Running an MVNO comes with its challenges, one of which is the risk of being targeted by SIM Box fraud. This type of fraud involves using a large number of SIM cards in a single device, called a SIM box, to route international calls as local calls, exploiting telecom networks and causing significant revenue loss.

A while ago, we helped an MVNO dealing with this exact issue. The manager of a small UK-based MVNO reached out with concerns about a sudden increase in new activations and skyrocketing call volumes. While these indicators initially seemed like signs of business success, the manager suspected something was off.

Our team quickly analyzed the CDRs and TDRs and discovered an alarming trend: many subscribers were making an unusually high number of calls to a large number of other subscribers. While an average user might call 2-3 different numbers per day, some were contacting 200-300 numbers.

Further investigation revealed that these high-call-volume accounts had been activated recently and were behaving differently from typical users. The MVNO decided to deactivate these suspicious accounts, but the fraudsters did not surrender and responded by activating new SIM cards and continuing their fraudulent activities.

The MVNO did not have the time or financial resources to implement a sophisticated anti-fraud solution as the fraudulent activities were causing continuous losses. To address this, we implemented a practical and straightforward solution. On an hourly basis, we sent reports to the MVNO’s customer care team with lists of suspicious subscribers. These accounts were then manually reviewed and suspended after additional checks. It became too costly for the fraudsters to continue their scheme, and after five days of monitoring, no new suspicious SIM cards were detected. The MVNO manager was extremely grateful for this straightforward yet effective solution that resolved a major problem quickly.