Cellcom, a telecommunications provider based in Wisconsin, has confirmed a cyberattack caused a major service disruption that began nearly a week ago. Thousands of customers have been affected across its network.
The outage started on Wednesday, May 14, and mainly impacted voice calls and SMS services. Many users could not make calls or send texts during this period.
Details of the Cyberattack
According to Cellcom CEO Brighid Riordan, the cyberattack targeted the company’s voice and SMS systems. Other services remained operational.
“The cyber incident that we’re experiencing is segmented to the voice and texting part of your service,” Riordan said in a video message released on May 20.
The attack compromised parts of Cellcom’s Public Switched Telephone Network (PSTN), specifically affecting the Session Initiation Protocol (SIP) systems responsible for managing calls.
Technical teams have worked hard to restore service. By May 19, SMS texting and voice calls within the Cellcom network were working again. This was achieved by restoring the SS7 SMS gateway, which routes messages between networks.
However, calls and messages between Cellcom and other carriers remain unreliable because the attack damaged the network components that handle cross-carrier communication.
Customers have been advised to temporarily switch their phones to Airplane Mode and then back to normal to reconnect with the network after partial restoration.
Impact and Customer Support
The outage caused serious disruptions. Customers reported missed family calls, lost business opportunities, and even missed job interviews. In response, Cellcom has launched a customer support plan.
“As a gesture of accountability and thanks, we are covering outage service fees for customers who stay with us,” the company announced. These credits will appear on future bills.
CEO Riordan acknowledged the frustration caused by the outage and apologized publicly.
“We know this disruption has caused frustration and, for some, real hardship — and for that, I am truly sorry,” she said.
Cellcom also warned customers to watch out for scams exploiting the situation. The company stressed that it will never ask customers for personal information or account details via unsolicited contact.
Response and Security Measures
Cellcom has activated its cybersecurity protocols and is working with outside experts to investigate the breach. Authorities including the FBI and Wisconsin officials have been notified.
“We were prepared for this; we have protocols in place for such incidents, and we are executing them,” Riordan explained.
Despite the attack’s severity, Cellcom assures customers that their personal data remains safe. The breach affected only the network area handling calls and texts, separate from where sensitive customer information is stored.
This differs from recent incidents such as the SK Telecom breach, which went undetected for years and compromised millions of subscribers’ data.
Outlook for Full Service Restoration
Cellcom expects to fully restore all affected services by the end of this week. The company emphasized a careful and precise approach to recovery, prioritizing security over speed to prevent further damage.
“Every part of this recovery is being handled with care and precision,” Cellcom stated.
