Infostealers Explained: The Hidden Gateway to Ransomware

Cybercrime continues to rise at a fast pace, with global damages in 2025 projected to hit $10.5 trillion – which would make it the world’s third-largest ‘economy’ if it were a country. Yet despite the ever-growing sophistication of attackers, behind the headlines of even the biggest data breaches often lies something surprisingly simple: a compromised password.

Stolen login details provide attackers with an easy way in, giving them the foothold they need to escalate their attacks and do further damage. Once in, they can move through networks to steal sensitive data or unleash ransomware. One of the most effective tools for gathering these credentials is infostealer malware, which is designed to quietly collect and transmit logins while leaving businesses unaware of the threat until it is too late. Therefore, it’s a threat all firms need to be aware of in order to improve their cyber resiliency.

Infostealers are a type of malware specifically designed to harvest sensitive information from infected devices. They typically target stored credentials, authentication tokens, browser cookies, system information and even cryptocurrency wallets. Once installed, these tools silently collect data and send it to attacker-controlled servers.

In 2025, infostealers were responsible for the theft of over 1.8 billion credentials across more than 5.8 million devices, according to research by Flashpoint. This marks an 800 percent increase from the previous six months, illustrating a growing problem. This data is frequently packaged and sold on dark web marketplaces or used directly by threat actors to infiltrate corporate systems.

The real danger lies in what comes next. With stolen logins, attackers can bypass perimeter security, escalate privileges and launch larger attacks such as ransomware or data exfiltration. For many modern breaches, infostealers are not the end goal but the quiet beginning.

Infostealers typically enter systems through phishing emails, malicious website redirects, fake software downloads or compromised ads known as malvertising. Once a user clicks the wrong link or installs a tainted file, the malware embeds itself on the device and begins silently extracting valuable data. This can include saved passwords, session tokens, autofill details, browser history and device metadata.

The stolen data is then exfiltrated to remote servers controlled by the attacker, often encrypted to avoid detection. From there, it is either used directly for identity theft, financial fraud and business intrusion or sold in bulk on dark web marketplaces.

This underground trade in harvested credentials fuels further attacks, enabling cybercriminals to buy access to business networks or impersonate legitimate users. In many cases, these credentials are the first step toward much larger incidents such as ransomware deployment or full-scale system compromise.

Infostealers are favored by cybercriminals because they offer a low-cost, high-reward way to access valuable data with minimal effort. Often sold as ready-to-use toolkits on underground forums, they can be deployed by even inexperienced attackers to harvest credentials at scale.

In turn, these stolen details may be sold to larger ransomware groups or initial access brokers who have more sophisticated capabilities. They can use this information to infiltrate corporate networks undetected.

For these more advanced actors, infostealers are the first step in a broader attack chain. Once access is secured, criminals can move laterally through systems, escalate privileges, encrypt or delete information or exfiltrate data. This makes infostealers a critical enabler of high-impact breaches such as double extortion ransomware, offering a quiet, hard-to-detect way to find the most valuable digital assets and gain control before launching more disruptive attacks.

While infostealers often operate silently, the long-term damage they enable can be huge. That’s why preventing them requires a layered approach – one that not only aims to reduce the chance of initial infection, but can also minimize the impact if stolen credentials are used to infiltrate networks.

Businesses need to prioritize proactive data security management, focusing not just on keeping attackers out, but on stopping them from moving deeper into the network if they get in and exfiltrating data. The following best practices are essential:

• Enforce strong password hygiene: As well as avoiding easily guessed or shared passwords, employees should never reuse passwords from personal accounts. A single reused login from a compromised third-party site can give attackers an entry point into business systems.
• Implement regular anti-phishing training: Many infostealers are delivered through phishing emails. Training staff to spot suspicious messages can stop attacks before they begin.
• Use multi-factor authentication (MFA): Even if passwords are stolen, MFA adds a critical extra layer that blocks access without a second verification step.
• Adopt zero trust principles: Assume no user or device is safe until verified and consider continuous verification to prevent unauthorized access and spot infiltrations early.
• Continuously monitor for abnormal activity: Keep watch for signs of lateral movement or attempted data exfiltration, which can signal a compromised system.
• Use ADX to prevent data theft: Dedicated anti data exfiltration technology can prevent information harvested by infostealers from leaving the network, as well as block wider ransomware data exfiltration attempts.

Infostealers represent a growing threat that businesses can’t afford to ignore. With stolen credentials often serving as a gateway to larger attacks, it’s critical to adopt a proactive defense. Organizations should assume that network perimeters will be breached and focus on detecting intrusions early using tools that can identify suspicious behavior and block data exfiltration in progress.