Cellcom confirms cyberattack behind week-long voice and text outage in Wisconsin

Cellcom, a regional wireless carrier serving Wisconsin and Michigan's Upper Peninsula, confirmed in the week of 19 May 2025 that a cyberattack was behind an outage that had left customers unable to make voice calls or send text messages. The disruption began on 14 May, with SMS service failing the following day, and ran for about a week.

Chief executive Brighid Riordan said the incident was confined to a part of the network handling voice and texting and was separate from the systems that store sensitive customer records. She told customers the company had no evidence that their personal information, names, addresses or financial information had been affected. Data service continued to work throughout.

The company brought in outside cybersecurity specialists and notified the FBI and Wisconsin state officials. Texting and Cellcom-to-Cellcom calling were restored by Monday 19 May, and the carrier said it expected the remaining services back by the end of that week.

Cellcom did not describe how the attack was carried out, and no group claimed responsibility. Security Affairs noted that the pattern was consistent with a ransomware incident but that the carrier had not confirmed ransomware. A spokesperson declined to say how many subscribers had lost service.