US wireless carrier T-Mobile is investigating a 24-hour breach involving the accounts of 37 million of its cell phone users.
On January 5, security teams identified malicious activity within the big three carrier's network, according to the Reuters news agency.
T-Mobile announced the ongoing investigation today and reported that no financial information belonging to their customers was compromised during the event.
"Our investigation is still ongoing, but the malicious activity appears to be fully contained at this time, and there is currently no evidence that the bad actor was able to breach or compromise our systems or our network," the Washington based company told Reuters.
The incident, which T-Mobile said was caught and isolated within the same day, involved nearly a third of all customers, including both contract and prepaid accounts.
T-Mobile sent this tweet to one disgruntled customer looking for guidance:
We are in the process of reaching out to all impacted customers. If you're impacted, you will be notified via your online T-Mobile account and billing statement. Send me a DM so we can take a look at what's happening with your device. ^Erica Ramos https://t.co/8DIvLVByJjundefined T-Mobile Help (@TMobileHelp) January 19, 2023
T-Mobile has suffered nearly half a dozen large-scale attacks within the past few years and this one is also expected to cost the company millions, reported Reuters.
A 2021 attack affecting over 76 million customers eventually cost the company roughly half a million dollars between security upgrades, government fines, and legal fees.
T-Mobile shares were reported to drop by over 2% after the announcement.
Only basic information, such as customer names, billing addresses, emails, and phone numbers were compromised during the incident, T-Mobile said.
The malicious bad actors have not been identified.