Following reports of a data breach over the weekend, T-Mobile has confirmed it’s investigating a cybersecurity incident. In an update published on Monday, the company said someone gained unauthorized access to its computer systems, but that it has yet to determine if any customer data was stolen.

“We are confident that the entry point used to gain access has been closed, and we are continuing our deep technical review of the situation across our systems to identify the nature of any data that was illegally accessed,” the carrier said.

When Motherboard first broke the news of the data breach on Sunday, the information of about 30 million T-Mobile customers was on sale on the dark web for about $270,000 in Bitcoin. A hacker told the outlet they had obtained social security and IMEI numbers connected to more than 100 million people. As of the second quarter of 2021, T-Mobile had 104.7 million subscribers. The carrier said it could not “confirm the reported number of records affected or the validity of statements made by others” until it completes its investigation. Once it knows more about the situation, T-Mobile promises to proactively contact customers.