T-Mobile today disclosed a data breach affecting tens of millions of customer accounts, its second major data exposure in as many years. In a filing with federal regulators, T-Mobile said an investigation determined that someone abused its systems to harvest subscriber data tied to approximately 37 million current customer accounts.

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In a filing today with the U.S. Securities and Exchange Commission, T-Mobile said a “bad actor” abused an application programming interface (API) to hoover up data on roughly 37 million current postpaid and prepaid customer accounts. The data stolen included customer name, billing address, email, phone number, date of birth, T-Mobile account number, as well as information on the number of customer lines and plan features.

APIs are essentially instructions that allow applications to access data and interact with web databases. But left improperly secured, these APIs can be leveraged by malicious actors to mass-harvest information stored in those databases. In October, mobile provider Optus disclosed that hackers abused a poorly secured API to steal data on 10 million customers in Australia.

The company said it first learned of the incident on Jan. 5, 2022, and that an investigation determined the bad actor started abusing the API beginning around Nov. 25, 2022.

T-Mobile says it is in the process of notifying affected customers, and that no customer payment card data, passwords, Social Security numbers, driver’s license or other government ID numbers were exposed.

In August 2021, T-Mobile acknowledged that hackers made off with the names, dates of birth, Social Security numbers and driver’s license/ID information on more than 40 million current, former or prospective customers who applied for credit with the company. That breach came to light after a hacker began selling the records on a cybercrime forum.

Last year, T-Mobile agreed to pay $500 million to settle all class action lawsuits stemming from the 2021 breach. The company pledged to spend $150 million of that money toward beefing up its own cybersecurity.

In its filing with the SEC, T-Mobile suggested it was going to take years to fully realize the benefits of those cybersecurity improvements, even as it claimed that protecting customer data remains a top priority.

“As we have previously disclosed, in 2021, we commenced a substantial multi-year investment working with leading external cybersecurity experts to enhance our cybersecurity capabilities and transform our approach to cybersecurity,” the filing reads. “We have made substantial progress to date, and protecting our customers’ data remains a top priority.”

Despite this being the second major customer data spill in as many years, T-Mobile told the SEC the company does not expect this latest breach to have a material impact on its operations.

While that may seem like a daring thing to say in a data breach disclosure affecting a significant portion of your active customer base, consider that T-Mobile reported revenues of nearly $20 billion in the third quarter of 2022 alone. In that context, a few hundred million dollars every couple of years to make the class action lawyers go away is a drop in the bucket.

The settlement related to the 2021 breach says T-Mobile will make $350 million available to customers who file a claim. But here’s the catch: If you were affected by that 2021 breach and you haven’t filed a claim yet, please know that you have only three more days to do that.

If you were a T-Mobile customer affected by the 2021 incident, it is likely that T-Mobile has already made several efforts to notify you of your eligibility to file a claim, which includes a payout of at least $25, with the possibility of more for those who can document direct costs associated with the breach. OpenClassActions.com says the filing deadline is Jan. 23, 2023.

“If you opt for a cash payment you will receive an estimated $25.00,” the site explains. “If you reside in California, you will receive an estimated $100.00. Out of pocket losses can be reimbursed for up to $25,000.00. The amount that you claim from T-Mobile will be determined by the class action administrator based on how many people file a legitimate and timely claim form.”

There are currently no signs that hackers are selling this latest data haul from T-Mobile, but if the past is any teacher much of it will wind up posted online soon. It is a safe bet that scammers will use some of this information to target T-Mobile users with phishing messages, account takeovers and harassment.

T-Mobile customers should fully expect to see phishers taking advantage of public concern over the breach to impersonate the company — and possibly even send messages that include the recipient’s compromised account details to make the communications look more legitimate.

Data stolen and exposed in this breach may also be used for identity theft. Credit monitoring and ID theft protection services can help you recover from having your identity stolen, but most will do nothing to stop the ID theft from happening. If you want the maximum control over who should be able to view your credit or grant new lines of credit in your name, then a security freeze is your best option.

Regardless of which mobile provider you patronize, please consider removing your phone number from as many online accounts as you can. Many online services require you to provide a phone number upon registering an account, but in many cases that number can be removed from your profile afterwards.

Why do I suggest this? Many online services allow users to reset their passwords just by clicking a link sent via SMS, and this unfortunately widespread practice has turned mobile phone numbers into de facto identity documents. Which means losing control over your phone number thanks to an unauthorized SIM swap or mobile number port-out, divorce, job termination or financial crisis can be devastating.

The U.S. Department of Justice (DOJ) said today it seized the website and user database for RaidForums, an extremely popular English-language cybercrime forum that sold access to more than 10 billion consumer records stolen in some of the world’s largest data breaches since 2015. The DOJ also charged the alleged administrator of RaidForums — 21-year-old Diogo Santos Coelho, of Portugal — with six criminal counts, including conspiracy, access device fraud and aggravated identity theft.

The “raid” in RaidForums is a nod to the community’s humble beginnings in 2015, when it was primarily an online venue for organizing and supporting various forms of electronic harassment. According to the DOJ, that early activity included ‘raiding‘ — posting or sending an overwhelming volume of contact to a victim’s online communications medium — and ‘swatting,’ the practice of making false reports to public safety agencies of situations that would necessitate a significant, and immediate armed law enforcement response.”

But over the years as trading in hacked databases became big business, RaidForums emerged as the go-to place for English-speaking hackers to peddle their wares. Perhaps the most bustling marketplace within RaidForums was its “Leaks Market,” which described itself as a place to buy, sell, and trade hacked databases and leaks.

The government alleges Coelho and his forum administrator identity “Omnipotent” profited from the illicit activity on the platform by charging “escalating prices for membership tiers that offered greater access and features, including a top-tier ‘God’ membership status.”

“RaidForums also sold ‘credits’ that provided members access to privileged areas of the website and enabled members to ‘unlock’ and download stolen financial information, means of identification, and data from compromised databases, among other items,” the DOJ said in a written statement. “Members could also earn credits through other means, such as by posting instructions on how to commit certain illegal acts.”

Prosecutors say Coelho also personally sold stolen data on the platform, and that Omnipotent directly facilitated illicit transactions by operating a fee-based “Official Middleman” service, a kind of escrow or insurance service that denizens of RaidForums were encouraged to use when transacting with other criminals.

Investigators described multiple instances wherein undercover federal agents or confidential informants used Omnipotent’s escrow service to purchase huge tranches of data from one of Coelho’s alternate user  identities — meaning Coelho not only sold data he’d personally hacked but also further profited by insisting the transactions were handled through his own middleman service.

Not all of those undercover buys went as planned. One incident described in an affidavit by prosecutors (PDF) appears related to the sale of tens of millions of consumer records stolen last year from T-Mobile, although the government refers to the victim only as a major telecommunications company and wireless network operator in the United States.

On Aug. 11, 2021, an individual using the moniker “SubVirt” posted on RaidForums an offer to sell Social Security numbers, dates of birth and other records on more than 120 million people in the United States (SubVirt would later edit the sales thread to say 30 million records). Just days later, T-Mobile would acknowledge a data breach affecting 40 million current, former or prospective customers who applied for credit with the company.

The government says the victim firm hired a third-party to purchase the database and prevent it from being sold to cybercriminals. That third-party ultimately paid approximately $200,000 worth of bitcoin to the seller, with the agreement that the data would be destroyed after sale. “However, it appears the co-conspirators continued to attempt to sell the databases after the third-party’s purchase,” the affidavit alleges.

The FBI’s seizure of RaidForums was first reported by KrebsOnSecurity on Mar. 23, after a federal investigator confirmed rumors that the FBI had been secretly operating the RaidForums website for weeks.

Coelho landed on the radar of U.S. authorities in June 2018, when he tried to enter the United States at the Hartsfield-Jackson International Airport in Atlanta. The government obtained a warrant to search the electronic devices Coelho had in his luggage and found text messages, files and emails showing he was the RaidForums administrator Omnipotent.

“In an attempt to retrieve his items, Coelho called the lead FBI case agent on or around August 2, 2018, and used the email address unrivalled@pm.me to email the agent,” the government’s affidavit states. Investigators found this same address was used to register rf.ws and raid.lol, which Omnipotent announced on the forum would serve as alternative domain names for RaidForums in case the site’s primary domain was seized.

The DOJ said Coelho was arrested in the United Kingdom on January 31, at the United States’ request, and remains in custody pending the resolution of his extradition hearing. A statement from the U.K.’s National Crime Agency (NCA) said the RaidForum’s takedown was the result of “Operation Tourniquet,” which was carried out by the NCA in cooperation with the United Staes, Europol and four other countries, and resulted in “a number of linked arrests.”

A copy of the indictment against Coelho is available here (PDF).