Dark Web Password Leaks: Check and Protect Yourself

About 8 min read

When the news reports that hundreds of millions of passwords have been leaked, many people feel it has nothing to do with them. However, leaked passwords are traded - often with their hashes cracked - on an anonymous network called the dark web and used for real unauthorized access. According to the Identity Theft Resource Center 2024 report, 3,158 data breach incidents were disclosed worldwide in 2024, affecting approximately 340 million individuals. This trend continues in 2025, with large-scale breaches showing no signs of slowing down. Furthermore, Digital Shadows research indicates that over 24 billion leaked credentials are circulating on the dark web, roughly three times the world population. The spread of AI-powered automated credential stuffing tools is also accelerating the exploitation of leaked data. This article explains how the dark web works, how leaked data is exploited, and introduces concrete defenses using パスつく.com.

What Is the Dark Web

The internet can be broadly divided into three layers: the "surface web" accessible through regular search engines, the "deep web" consisting of login-required membership sites and databases, and the "dark web" that can only be accessed using specialized software such as Tor.

The dark web itself is technically neutral, but its high degree of anonymity has made it a breeding ground for illegal transactions. Stolen credit card information, personal data, and password databases are routinely traded, forming a cybercrime ecosystem. Communications on the Tor network are encrypted through multiple relay nodes, making it extremely difficult to identify the source. This technical characteristic is the fundamental reason why law enforcement crackdowns are so challenging.

The Reality of Leaked Data Trading

When companies or services suffer cyberattacks and their databases are leaked, attackers list the information on dark web marketplaces. Transactions are conducted using cryptocurrencies such as Bitcoin, making them difficult to trace.

The price of leaked data varies greatly depending on its content. Email and password sets are traded for just a few cents each, but when bank account or credit card information is included, prices can reach tens of dollars or more. Immediately after a large-scale breach, prices drop as data floods the market, but over time the value increases as datasets become "verified."

What makes this particularly serious is that once leaked data enters circulation, it is impossible to fully recover. Copies are infinitely replicated and fall into the hands of multiple attacker groups. Even years after a breach, the risk of exploitation remains if passwords have not been changed.

How Combo Lists Work and Their Threats

A combo list is a compilation of email addresses (or usernames) and passwords collected from multiple breach incidents into a single list. Attackers use these lists to automatically attempt logins across various services. This attack technique is called "credential stuffing."

Combo lists are effective because many users reuse passwords. The reality is that credentials leaked from one service work on other services in a surprisingly large number of cases. Attackers load millions of combo list entries into automated tools and attempt to breach large numbers of accounts in a short time.

More sophisticated attackers analyze patterns in leaked passwords to predict what users might change them to. For example, if "Password2023" was leaked, they will try "Password2024" or "Password2023!" Human-devised password change patterns are inherently predictable. It is important to note that simply appending a single digit or symbol to the end of a password is a pattern already registered in attack tool dictionaries and provides virtually no defensive benefit.

To learn more about credential stuffing, credential stuffing and password list attack guides (Amazon)can also be helpful.

How to Check If Your Information Has Been Leaked

There are ways to check whether your email address or password has been included in past breach incidents. Have I Been Pwned (haveibeenpwned.com) is a highly reliable service that allows you to search across past breach databases. Simply entering your email address reveals which breach incidents it was included in.

If a breach is confirmed, immediately change the password for the affected service. If you used the same password on other services, you need to change all of them to different passwords. A common misconception is that "it is fine if the leaked password is an old one," but attackers predict change patterns from past passwords, making it essential to switch to a completely random new password.

For specific steps on breach detection and response, data breach detection and response guides (Amazon)can also be helpful.

Defense Strategy: Using Random Passwords with パスつく.com

The most effective defense against combo lists and credential stuffing is to use completely random passwords for each service. パスつく.com generates passwords using cryptographically secure random numbers, ensuring no human habits or guessable patterns are included.

Key points for using パスつく.com as a dark web countermeasure:

• Generate a different password for every service, completely eliminating password reuse
• Use at least 16 characters including uppercase letters, lowercase letters, digits, and symbols
• Verify at least 80 bits of entropy using the パスつく.com strength meter
• Immediately regenerate passwords with パスつく.com for any service where a breach is discovered
• Store generated passwords in a password manager instead of relying on memory

Random passwords generated by パスつく.com have virtually zero chance of appearing in combo lists. Manage your generated passwords with a password manager. Even if one service is breached, completely different passwords are set for other services, breaking the chain of damage. Understanding the risks of password reuse is essential. Since all password generation processing is completed within the browser, there is no risk of the generated passwords themselves being leaked externally. For specific steps to take when a breach is discovered, see also What to Do When a Data Breach Occurs and personal incident response.

Breach Protection Self-Checklist

Review the following items to assess your defenses against the exploitation of leaked data on the dark web.

• Have you checked your email address for breaches on Have I Been Pwned?
• Have you changed passwords for all services where breaches were confirmed?
• Are you using different passwords for every service?
• Are your passwords random strings of at least 16 characters?
• Have you set up two-factor authentication for important accounts?
• Are you centrally managing credentials with a password manager?
• Have you registered for breach notification services (such as Have I Been Pwned email alerts)?

What You Can Do Right Now

1. Check your email address for breaches on Have I Been Pwned (haveibeenpwned.com) and register for breach notification emails
2. Immediately change passwords for breached services to random passwords of at least 16 characters generated by パスつく.com
3. List all services where you reuse passwords and sequentially change them all to different passwords
4. Set up two-factor authentication for important accounts (email, financial services)
5. Adopt a password manager and establish a system for centrally managing all credentials

Frequently Asked Questions

Can I check if my password is being sold on the dark web?

You can check at Have I Been Pwned (haveibeenpwned.com) by searching your email address. There is no need to access the dark web directly. Using legitimate monitoring services like this is the safe approach.

What happens when passwords are leaked to the dark web?

Leaked passwords are compiled into lists and used for credential stuffing (automated login attempts on other services). They are sold in sets ranging from a few dollars to thousands of accounts, and buyers use automated tools to attempt mass unauthorized logins. Password reuse causes cascading damage.

What can individuals do to prevent their passwords from ending up on the dark web?

You cannot prevent breaches on the service side, but you can minimize damage. Use a different random password for every service and enable two-factor authentication. Even if one service is breached, the impact on your other accounts will be zero.