Spanish telecommunications giant Telefonica recently fell victim to a significant cybersecurity breach, showing that even large organizations can be vulnerable. The event highlights how important it is to maintain strong defenses, especially against infostealers, which are designed specifically to steal information.

The Breach: What Happened?

This month (January 2025), Telefonica confirmed unauthorized access to its internal Jira ticketing system. The breach, orchestrated by a group of attackers allegedly linked to the Hellcat ransomware group, resulted in the theft of approximately 2.3 GB of sensitive data. The stolen information included:

• 24,000 employee emails and names
• 500,000 Jira issues and summaries
• 5,000 internal documents
• 236,493 lines of customer data

The Attack Vector: Infostealer Malware

The breach was facilitated by infostealer malware, a type of malicious software designed to harvest sensitive information such as login credentials from infected devices. Numerous employees were reported to be compromised, providing attackers with critical credentials for initial access

• 469 employee credentials on Telefonica’s domain were compromised.
• 469 employee credentials on Telefonica’s domain were compromised.
• 469 employee credentials on Telefonica’s domain were compromised.
• 469 employee credentials on Telefonica’s domain were compromised.

According to estimates, there are now more than 30 billion stolen credentials circulating on the dark web. Most of them are being actively traded, sold, and used for cyberattacks such as account takeovers and fraud. The most dangerous part about this is that many organizations have no clue that their credentials are compromised until it’s too late. 

So how do credentials end up on the dark web in the first place, and what steps can you take to find out if yours have been compromised? Let’s break it down.

How do credentials end up on the dark web?

Credentials don’t just randomly show up for sale on dark web marketplaces, although it may seem like it for organizations with no visibility into underground cybercriminal activity.

Many new Twilight Cyber customers are left dumbfounded when they discover that their credentials have been circulating on the dark web for months, sometimes even years, without their knowledge.

In reality, the credentials find themselves there for one of three primary reasons:

1. Infostealers
   Malware designed to steal credentials, cookies, and other sensitive data is widely used by cybercriminals. Infostealers operate silently, capturing login information stored in browsers or extracted from clipboard data. Once stolen, these credentials are sold on the dark web or used for further attacks.
2. Data breaches
   Headlines like “Major Software Provider Suffers Data Breach, Millions of Customer Records Exposed” are not just sensational news stories. Real organizations and people are affected, potentially leaking their sensitive data, including credentials.
3. Weak passwords
   Employees may be reusing or using weak passwords, making them susceptible to brute forcing and credential stuffing attacks.
4. Phishing attacks
   Cybercriminals trick individuals into unknowingly handing over their credentials through phishing emails and fake login pages. A well-crafted phishing email can impersonate a trusted entity, such as a widely used service, convincing users to enter their login details.

Signs your credentials might be on the dark web

Warning Signs & Red Flags

Stolen credentials don’t always lead to immediate account takeovers. Sometimes, they sit undetected on the dark web for months or longer before being exploited. However, there are warning signs that could indicate your credentials have been compromised. If you notice any of the following, your accounts may already be at risk:

Failed login attempts and account lockouts

Repeated failed login attempts on your accounts, unexpected password reset prompts or even account lockouts are solid indicators that someone is trying to gain unauthorized access using stolen or guessed credentials.

Security alerts from your accounts

Many platforms send security notifications for suspicious activity, such as logins from unfamiliar locations, new devices, or multiple failed authentication attempts. If you receive an alert that you didn’t trigger, it’s a strong sign that your credentials may be in the wrong hands.

Note: Be careful, sometimes cybercriminals create fake security alerts to get you to expose your credentials. Always verify the authenticity of the sender and message.

Increase in phishing activity

A sudden spike in phishing emails, scam messages, or fake login requests can be a red flag that cybercriminals have obtained your credentials. Attackers often use stolen login details to launch targeted phishing campaigns, tricking you into revealing more sensitive information or resetting your password on a fraudulent site.

A third-party has suffered a security breach

Even if your organization hasn’t experienced a direct cyberattack, your credentials can still be exposed if a third-party service you use is breached. Cloud services and software providers that store user login information are particularly vulnerable. If one of these platforms suffers a data breach, your credentials may end up on the dark web without your knowledge.

If you receive a notification from a vendor about a security incident, assume your credentials are at risk, especially if you reuse passwords across multiple accounts. 

For more details about the risks of reusing passwords, read our blog.

The value of dark web monitoring tools

Without dark web monitoring, detecting compromised credentials is a guessing game. You may notice that something suspicious is happening, but but have no way of knowing which credentials are exposed, which machine they were leaked from, where they were leaked, or how cybercriminals might be using them.

Dark web monitoring eliminates this uncertainty by providing real-time visibility into credential leaks. Instead of waiting for signs of an attack, these tools proactively scan underground marketplaces, breach dumps, and hacker forums to identify exposed credentials linked to your organization.

This intelligence allows organizations to take immediate action to mitigate risks, whether that means enforcing password resets, revoking compromised access, or strengthening authentication processes.

Protect yourself from credential leaks with Twilight

Twilight Cyber not only detects compromised machines and stolen data in real time but also enables automated remediation to neutralize threats before they can be exploited. Our platform continuously monitors for indicators of compromise, providing actionable insights and mitigation to strengthen your security posture.

Spanish telecommunications giant Telefonica recently fell victim to a significant cybersecurity breach, showing that even large organizations can be vulnerable. The event highlights how important it is to maintain strong defenses, especially against infostealers, which are designed specifically to steal information.

The Breach: What Happened?

This month (January 2025), Telefonica confirmed unauthorized access to its internal Jira ticketing system. The breach, orchestrated by a group of attackers allegedly linked to the Hellcat ransomware group, resulted in the theft of approximately 2.3 GB of sensitive data. The stolen information included:

• 24,000 employee emails and names
• 500,000 Jira issues and summaries
• 5,000 internal documents
• 236,493 lines of customer data

The Attack Vector: Infostealer Malware

The breach was facilitated by infostealer malware, a type of malicious software designed to harvest sensitive information such as login credentials from infected devices. Numerous employees were reported to be compromised, providing attackers with critical credentials for initial access

• 469 employee credentials on Telefonica’s domain were compromised.
• 469 employee credentials on Telefonica’s domain were compromised.
• 469 employee credentials on Telefonica’s domain were compromised.
• 469 employee credentials on Telefonica’s domain were compromised.

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