T-Mobile is looking into a claim that data stolen from its servers is being sold online.

T-Mobile confirmed on Monday that some of its data may have been illegally accessed. The mobile carrier is still investigating a post on a forum that claimed to be selling the personal data of more than 100 million people swiped from T-Mobile's servers. (Here are some steps you can take to protect your data right now.)

"We have not yet determined that there is any personal customer data involved," T-Mobile said in a release. "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 data breach included information such as Social Security numbers, phone numbers, names, physical addresses and driver's license information, according to Vice, which reported the security breach claim earlier on Sunday. The forum post doesn't mention T-Mobile by name, but the seller told Vice's Motherboard that the data came from T-Mobile servers.

The seller is requesting 6 Bitcoin (about $277,000) for a subset of the data containing 30 million Social Security numbers and driver's licenses, while the rest of the data is being sold privately, according to the Vice report.