“We’re writing to let you know that the primary network provider for Google Fi recently informed us there has been suspicious activity relating to a third-party system that contains a limited amount of Google Fi customer data,” Google wrote in an email to Fi users.

The search giant didn’t specifically name T-Mobile in the email, but the carrier is indeed Fi’s “primary network provider” in the US.

User data affected by the breach?

Google added that the third-party system in question was used for Google Fi customer support and contained “limited” user data. This information includes the date of account activation, service plan information, your SIM card serial number, and account status (active/inactive).

The company stressed that the affected data didn’t include names, date of birth, email addresses, payment info, social security numbers, government IDs, Google Fi passwords/PINs, or the contents of texts/calls. It also confirmed that there was no access to Google’s systems or systems overseen by the search giant.

Google says it’s worked with T-Mobile to better secure the data on that third-party system. Nevertheless, the incident shows one downside of Fi’s MVNO approach, as it’s forced to rely on carrier partners to safeguard some user data. Here’s hoping Fi’s data is safe from the next inevitable T-Mobile breach.