Google Fi has sent an email to customers to disclose that their account data was included in the more than 37 million customer records stolen from T-Mobile in November 2022.

Google Fi is a wireless plan that runs much of its service over T-Mobile networks.

Details on Google Fi customers, including phone number, SIM serial card number, and service plan details were among the stolen T-Mobile data. 

Google added in its email that the compromised information didn’t contain “your name, date of birth, email address, payment card information, Social Security or tax IDs, driver’s license or other form of government ID, or financial account information, passwords or PINs that you may use for Google Fi or the contents of any SMS messages or calls.”

However, Lior Yaari, CEO and co-founder of Grip Security, noted that potential cyberattackers can still do a lot of damage via SIM-swapping, by having access to the users’ phone numbers and SIM serial card numbers.

“At minimum, affected customers should consider changing out their SIM card to protect themselves,” he said via email. “Once the hackers take over your phone number, they can use it for illicit purposes, or even bypass two-factor authentication that uses SMS.”

Google Fi has not noted how many customers are affected. 

“Given the serious nature and impact of the breach, it’s surprising that Google has not disclosed the number of customers impacted, like what we have seen in other major breaches,” Yaari said. Google did not immediately return a request for comment.

The latest T-Mobile data breach marks the second in two years for the mobile carrier.