Cyber criminals don’t always need to break into a system using brute force or sophisticated exploits. Sometimes, all it takes is a single careless click to hand over everything they need.
Once seen as a niche threat, infostealers are now a common feature in cyber attacks against both individuals and businesses. In this post, we break down what infostealers are, how they work, and how you can reduce your risk of falling victim.
What is an infostealer?
An infostealer is a type of malware specifically designed to collect and extract information from an infected device. This typically includes usernames, passwords, browser cookies, credit card details, and other sensitive files or credentials.
The data is often sent back to a remote command-and-control (C2) server controlled by the attacker. From there, it may be used for further attacks, sold on the dark web, or used to impersonate the victim and access corporate systems.
What sets infostealers apart is their speed and silence. Many can complete their task in under a minute, often without leaving any visible trace on the machine. By the time the victim notices something is wrong, the damage is already done.
How do infostealers work?
Infostealers typically enter systems in the same ways most malware does via phishing emails, malicious links, cracked software downloads, or poisoned adverts on legitimate websites. Once installed, the malware runs quietly in the background, extracting information in several ways:
- Keylogging - Records every keystroke, capturing login details, card numbers and typed messages.
- Form grabbing - Intercepts data entered into online forms before it is encrypted.
- Cookie theft - Steals browser cookies and session tokens to bypass logins.
- Clipboard monitoring - Watches for and steals data copied to the clipboard, such as passwords or cryptocurrency wallet addresses.
- File harvesting - Scans local files, documents and configuration data for sensitive content.
- Screen captures - Takes screenshots at specific intervals or during certain activities.
- System profiling - Collects system information, such as installed software and security tools, to tailor attacks or avoid detection.
In more sophisticated campaigns, the malware can even detect if it's running in a sandboxed or monitored environment and remain dormant to avoid triggering alarms.
Why should businesses be concerned?
Infostealers don’t just pose a risk to individual users. When deployed on corporate networks, they can result in:
- Credential compromise - Single sign-on (SSO) and shared systems mean that one stolen login can give attackers access to a broad range of internal tools.
- Business email compromise (BEC) - Access to email accounts enables fraud, invoice scams and further social engineering attacks.
- Customer data theft - If stolen files contain customer details, the business could face serious reputational and regulatory consequences.
- Stepping stone attacks - Attackers often use stolen credentials from one company to target partners or suppliers, increasing the blast radius.
Infostealers are frequently part of broader toolkits, so they are often just the first step in a longer chain of attack that might end in ransomware or extortion.
How widespread is the problem?
The numbers are hard to ignore. Infostealers were the cause of nearly a quarter (24%) of all cyber incidents in 2024 and it’s predicted that this will continue to grow.1
Where does the stolen data go?
Once extracted, the stolen data is usually sent to a central server or traded on dark web marketplaces. Some attackers use automated bots on platforms like Telegram to sell credentials by brand or domain. A buyer can request all logins for a specific company, pay a small fee, and receive full access within minutes.
This data often fuels further attacks, such as:
- Credential stuffing - Automated attempts to reuse stolen passwords across multiple services.
- Phishing campaigns - Using stolen information to craft convincing phishing emails.
- Targeted ransomware - Attackers use data to identify high-value targets within organisations.
- Financial fraud - Bank and credit card details are used for direct theft or resold.
How reliable is the stolen data?
Interestingly, not all data stolen by infostealers is useful. Many credentials are outdated, mis-typed, or belong to previously compromised systems. Sometimes attackers themselves are victims, and malware logs can contain data from other criminals testing stolen passwords on infected machines.
This doesn’t reduce the threat it only reinforces the scale of the problem. Stolen data is messy, but even one valid login can be enough to breach a company.
How to protect yourself and your organisation
There is no single fix for infostealers, but the following steps significantly reduce risk:
- Update software continuously
Exploits often rely on outdated browsers, plugins, or third-party tools. - Use a password manager
Avoid saving credentials in your browser. A dedicated password manager encrypts and isolates your login data, making it harder for infostealers to access. - Implement multi-factor authentication (MFA)
Even if credentials are stolen, MFA blocks most unauthorised access but only if session hijacking isn’t possible. - Limit data storage in browsers
Discourage employees from storing credentials in browsers, which are common targets for infostealers. - Use threat intelligence and dark web monitoring
Monitor for leaked credentials tied to your domain or executive emails. Respond quickly if they appear. - Educate staff and reinforce policies
Many infections start with user error. Regular training on phishing, software downloads, and device use is essential. - Adopt a Zero Trust mindset
Assume no device or user is trustworthy by default. Enforce strict access controls, verify identities continuously, and segment systems to limit lateral movement if malware does land.
Final thoughts
Infostealers aren't new, but the scale and sophistication of today’s attacks are a different beast. The days of opportunistic, clumsy malware are long gone. What we’re seeing now is highly automated, often rented infrastructure, capable of harvesting credentials in seconds and selling them just as fast.
For businesses, this means the fallout isn’t limited to a single compromised account it’s access to systems, client data, financials, and potentially the entire supply chain. One infection can open the door to a much larger breach.
If you want to discuss this further, please get in touch.