Google has notified customers using its Google Fi cell service that their personal data may have been stolen in a recent cyberattack, which is believed to be in connection with a T-Mobile data breach earlier this month. In an email sent to Google Fi customers on Monday, obtained by Android Police, Google said that the cell network’s primary network provider had become aware of suspicious activity in a system containing Google Fi customer data. 

Google Fi is an MVNO that uses T-Mobile’s network for the majority of its connections alongside US Cellular, but Google doesn’t explicitly name T-Mobile as its primary service provider within the email. We have reached out to Google for clarification and will update this story should we hear back.

Google says that hackers may have accessed limited customer information via the compromised system, which includes phone numbers, SIM card serial numbers, account status, and mobile service plan data. The system did not contain personal customer information such as names, email addresses, payment card data, government IDs, passwords, or pin numbers. Google reassured customers that no further action is required by Fi users, and that there was no unauthorized access to Google’s own systems or any systems overseen directly by Google.

Both the timing of the announcement and Google Fi’s relationship with T-Mobile suggest that this breach directly links to a cyber attack earlier this month that impacted 37 million T-Mobile customers  — the eighth T-Mobile hack since 2018. Google has not disclosed how many Google Fi customers may have been impacted by the breach, and the company has yet to provide any information regarding how many users subscribe to the Google Fi service.