Learn how to check if your company’s data has been exposed in a breach and what to do about it.
• Leaked credentials are the biggest risk, but session tokens from stealer logs are catching up fast. They bypass MFA entirely, and most teams don’t monitor for them.
• Third-party breaches are the blind spot. Your vendor gets hit with ransomware, and your data leaks with theirs. Check vendor exposure, not just your own domains.
• Finding a breach is only half the job. If you don’t have a response process ready (reset passwords, revoke sessions, check forwarding rules), the discovery doesn’t help you.
• One-time breach checks catch what’s already leaked. Continuous monitoring catches new leaks as they happen, often before attackers get around to using them.
Your employees’ credentials are probably for sale on a dark web market right now. The question is whether you’ll find them before an attacker does.
Data leaks happen through phishing and infostealer malware. Third-party breaches expose even more. Once credentials are out, attackers use them for credential stuffing and account takeovers.
Most companies don’t find out about breaches until it’s too late. By then, attackers have already logged in.
This guide walks you through how to search for your breached data, what to look for, and how to respond.
If you’re searching for your company’s breached data, you need to know what to look for. Not all leaks are the same.
Here’s what you need to understand about how data gets leaked and what matters most.
Data breach is an incident where sensitive information is exposed to unauthorized parties. Breaches can happen through hacking and malware, or through third-party vendor compromise. The exposed data typically includes login credentials and personal information.
Usernames and passwords are the most exploitable type of leaked data. According to the Verizon 2025 DBIR, 88% of basic web application breaches involved stolen credentials.
Stolen credentials come from two main sources: third-party breaches and infostealer malware.
Third-party breaches used to be the primary source. But attackers have shifted to stealer logs for a simple reason: by the time a breach surfaces on the dark web, most victims have already reset their passwords. And modern apps use strong hashing algorithms like Bcrypt that make cracked passwords harder to get.
Stealer logs are different. Infostealer malware installed on a device grabs credentials in plaintext before they’re encrypted. The malware captures everything saved in the browser, including passwords and autofill data. Even if you use a password manager and generate strong passwords, an infected device hands them to attackers in plaintext.
These logs get posted to dark web markets within hours. Attackers also combine breach data with stealer logs to create combo lists for credential stuffing attacks.
Session tokens are one of the most overlooked types of leaked data. And they’re getting more dangerous.
Stealer logs don’t just grab passwords. They also capture session cookies. If an attacker has a valid session token, they can bypass both the login page and MFA. They’re already authenticated.
This type of attack is growing fast, especially on YouTube where creators get targeted by cookie-theft malware.
As passwordless authentication becomes more common, session token theft will replace credential theft as the primary attack vector.
Ransomware attacks don’t just encrypt your files. Most ransomware groups now steal data before encrypting it and post it on leak sites if you don’t pay.
This means internal documents and customer data can end up publicly available on the dark web. It happens through misconfigured cloud storage and insider threats. Ransomware is the biggest driver. Lost or stolen devices add to the risk.
Here’s the part most teams miss: your data can leak through someone else’s breach.
If a vendor stores your data and gets hit with ransomware, your data gets leaked too. If a vendor employee’s device gets infected with stealer malware, the attacker gets credentials that may include access to your network.
That’s why you need to monitor not just your own domains but your vendors’ and customers’ exposure as well.
Here’s a step-by-step process for checking your company’s breach exposure.
Start with your primary email domain. Search for it across breach data and stealer logs to see which employee credentials have been exposed.
You can run a quick dark web scan to check your domain against known breach data. This gives you a snapshot of your current exposure.
Third-party breach data only tells part of the story. Stealer logs are where the fresh credentials live. Search for your domain in stealer log databases to find recently stolen passwords and session tokens.
You’ll see “stealer log” throughout this guide. Here’s what it means.
Stealer log is a file created by infostealer malware running on an infected device. It captures saved passwords and session cookies, plus browser autofill data. Attackers sell or share these logs on dark web markets, often within hours of the infection.
Search for your vendors’ domains too. If a vendor that has access to your systems shows up in breach data, those credentials could be used to access your network.
Pay special attention to vendors with VPN access or cloud admin roles on your systems.
Not every leaked credential is equally dangerous. Check whether the passwords are current. Check if the accounts have MFA enabled. Check if the credentials give access to sensitive systems.
Focus your response on high-risk credentials first: admin accounts and VPN access. Cloud infrastructure and email accounts come next.
A one-time data breach search tells you what’s leaked right now. But new data leaks happen every day. Set up data breach monitoring to get real-time alerts when your domains appear in new breach data or stealer logs.
Breachsense monitors dark web markets, infostealer channels, hacker forums, and ransomware leak sites for your company’s data. That includes leaked credentials, session tokens, corporate documents, and exposed databases. You get alerted when anything shows up so you can respond before attackers use it.
Finding leaked data is only useful if you act on it. Here’s what to do.
Force password resets for every account that appears in the breach data. Don’t just notify users. Force the reset. Users who get notified often ignore it or delay for days.
If session tokens were leaked, resetting the password isn’t enough. Revoke all active sessions for the affected accounts. Otherwise the attacker can keep using the stolen session token even after the password changes.
Attackers who’ve already logged in often set up persistence mechanisms. Check for email forwarding rules and new OAuth app authorizations created after the breach window.
Figure out how the credentials were stolen. If they came from a third-party breach, the fix is a password reset. If they came from a stealer log, the source device is infected. It needs to be isolated and reimaged. According to CISA’s incident response guidance, containing the source is just as important as resetting credentials.
If your vendor’s credentials were in the breach data, contact them immediately. Ask what access those credentials provided and whether they’ve been rotated. Don’t wait for the vendor to notify you.
One-time data breach checks have a shelf life. New stealer logs hit dark web markets daily. Ransomware groups post new victims weekly. Your exposure changes constantly.
Continuous monitoring works by scanning dark web markets and stealer log channels for your company’s data on an ongoing basis. It also watches ransomware leak sites for vendor exposure. When a match appears, you get an alert.
Here’s what continuous monitoring covers that one-time checks miss:
The difference between a one-time check and continuous monitoring is the difference between a snapshot and a security camera. The snapshot tells you what already happened. The camera catches threats as they appear.
Most security teams that adopt continuous monitoring find leaked credentials they didn’t know about within the first week. That initial data breach search surfaces the backlog. After that, real-time alerts catch new leaks as they happen, giving you hours to respond instead of months.
Data breach monitoring gives your team real-time alerts and API access to integrate directly into your SIEM or security workflows. It covers credentials, session tokens, ransomware data, and vendor exposure. You can automate responses and track exposure trends over time.
Finding your breached data is a matter of knowing where to look and checking regularly.
Search your corporate domains in breach data and stealer logs. Check your vendors’ exposure too. When you find leaked credentials, reset passwords and revoke sessions immediately. Then set up continuous monitoring so you catch the next leak before attackers do.
Check your dark web exposure to see if your company’s credentials are already on criminal markets.
Search for your corporate email domains in breach data and stealer logs. Dark web monitoring automates this by scanning criminal markets for your domains continuously. You can also run a one-time dark web scan for a quick check.
A data breach search engine lets you look up whether specific email addresses or domains appear in known breach data. Enterprise versions also search stealer logs and dark web markets. Security teams use them to find exposed credentials before attackers do.
The most common types are email addresses and passwords. But stealer logs also capture session tokens and browser cookies. Ransomware attacks can leak internal documents and customer data. What gets exposed depends on how the breach happened.
One-time checks miss new leaks. Stealer logs get posted to dark web markets daily, so your exposure changes constantly. Continuous monitoring with real-time alerts is the only way to catch new leaks as they appear. Set up data breach monitoring for automated alerts.
Free tools check a limited set of third-party breach data. They won’t show you stealer logs or session tokens. For enterprise security, you need a platform that monitors dark web markets and criminal channels where stolen data actually gets sold.
Reset the compromised passwords immediately. Revoke any active sessions tied to those accounts. Check for email forwarding rules attackers may have set up. Then investigate how the credentials were stolen. If they came from a stealer log, the device is infected and needs to be wiped.
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