Teléfonica victim of a new data breach, hacker claims

A hacker going by the name “Rey” claims to have stolen 106GB of data from Teléfonica. The Spanish telecommunications company says it's nothing more than an extortion attempt.

In a post on Elon Musk’s social media platform X, Rey declared that Teléfonica denies that 106GB of data was stolen from the company’s internal network. Therefore, the hacker says he will release 5GB of data as proof.

“Soon, I will publish the full file tree, and over the next few weeks, if Teléfonica does not comply, the entire archive will be released ;)” the attacker states.

According to BleepingComputer, Rey has released a little over 20,000 files to prove the data breach actually occurred.

The hacker told the tech news outlet that the breach took place on May 30th, 2025, and that he was able to exfiltrate company data for 12 hours before getting noticed by Teléfonica’s IT employees.

In addition, Rey says he stole a total of 385,311 files, totaling 106.3GB of internal data. This includes internal communication (tickets, emails), purchase orders, invoices from business partners, internal logs, customer records, and employee data.

Teléfonica hasn’t acknowledged the breach, but an employee dismisses the incident as an extortion attempt using outdated information from a previous known incident.

Rey is a known member of a ransomware operation called HellCat Ransomware. In January 2025, the hacking group claimed to have successfully breached Teléfonica’s company network through an internal Jira development and ticketing server and stolen customer information.

HellCat Ransomware doesn’t extort the companies it breaches. Instead, it will leak all exfiltrated data if it doesn’t acknowledge the breach.

Telefónica is one of the largest telephone operators and mobile network providers in the world. The Spanish telecommunications company employs over 100,000 employees. Telefónica recorded a revenue of $40.5 billion in 2024 and a gross profit of almost $20.5 billion.