T-Mobile announced a data breach on Monday after a hacking organization claimed to have gotten records of 100 million T-Mobile customers in the United States and sold some of the information on the dark web. The US wireless carrier said it couldn't say how many users were affected, but that it has started a "deep technical review of the situation across our systems to identify the nature of any data that was illegally accessed."

T-Mobile is the brand name for the mobile communications companies of Deutsche Telekom AG, a German telecommunications firm. In the Czech Republic (T-Mobile Czech Republic), the Netherlands (T-Mobile Netherlands), Poland (T-Mobile Polska), and the United States (T-Mobile US). 

T-Mobile initially stated that it was investigating the hacker group's claim, but eventually admitted that at least some data had been acquired by the hackers. "We have determined that unauthorized access to some T-Mobile data occurred, however, we have not yet determined that there is any personal customer data involved," a company statement said. "We are confident that the entry point used to gain access has been closed."

T-Mobile said it was conducting its own investigation into the incident with the help of digital forensic experts and was collaborating with law enforcement. According to media sources citing postings on dark web forums, the enormous breach allegedly includes sensitive personal information such as social security and driver's license numbers. 

Motherboard was given access to some of the data, and the publication confirmed that it contained correct information on T-Mobile subscribers. The seller told Motherboard that they had hacked into various T-Mobile servers. A subset of the data, containing around 30 million social security numbers and driver's licenses, is being sold on the forum for six bitcoin, while the rest is being sold privately. At current exchange rates, six bitcoins are worth about $280,000. 

The seller told Motherboard, “I think they already found out because we lost access to the backdoored servers.” He was referring to T-Mobile’s potential response to the breach. T-Mobile appears to have thrown them out of the hacked systems, according to the seller, but they had already downloaded the data locally. They stated, "It's backed up in multiple places." 

The firm has also stated that once the situation is more understood, it would “proactively communicate” with customers and stakeholders, but that the investigation will “take some time.”