How info-stealing malware quietly undermines security

While ransomware still dominates headlines, infostealers have become one of the most widely used tools in the cyber-criminal playbook. Their purpose is simple: to quietly collect valuable data. That typically includes employee usernames and passwords, browser session tokens, cryptocurrency keys, autofill data and sensitive business information, all taken without obvious signs of compromise 

 

Why stolen credentials matter

 

The real danger lies in how this data is used. Stolen credentials are rarely a one-off prize. They are reused for account takeovers, fraud and espionage, or sold on to other attackers who use them as a stepping stone into larger, more damaging attacks later on 

 

In many cases, the initial infection is unremarkable. Infostealers are commonly delivered through phishing emails, malicious attachments, fake software updates, compromised websites or trojanised applications. From the victim’s point of view, it often looks like normal, everyday activity.

 

Once inside a system, these malware strains keep a low profile. They run quietly, harvesting data and sending it back to attacker-controlled infrastructure without slowing machines down or triggering obvious alerts. Many organisations only discover the compromise when stolen credentials start being abused elsewhere, long after the initial breach.

 

Designed to stay hidden

 

Infostealers have also benefited from being easy to buy and easy to deploy. Many are now sold through subscription-based malware-as-a-service models, complete with dashboards, updates and support. Tools such as Lumma Stealer allow attackers to tailor what they steal, whether that is browser cookies, saved passwords, cryptocurrency wallets or system details.

 

To stay hidden, modern infostealers rely on evasion techniques that make detection harder. These include delayed execution, hiding inside legitimate processes and avoiding automated analysis by only activating when real user behaviour is detected.

 

The data they collect rarely stays in one place. Instead, it is traded and resold across underground markets, often bundled with other stolen information. Corporate logins, cloud access tokens and cryptocurrency wallets are particularly valuable, helping to sustain a thriving underground economy built around stolen identities.

 

As a result, infostealers now sit behind a large proportion of cyber-crime activity. They quietly enable business email compromise, financial fraud, ransomware attacks and long-term espionage, even though they attract far less attention than more disruptive threats.

 

Why spotting an infection is so difficult

 

Detecting an infostealer infection is difficult by design. There are often no obvious warning signs. Instead, organisations may start to notice unusual login behaviour, unexpected password resets or access attempts from unfamiliar devices and locations.

This makes defence a matter of layers rather than single controls. User awareness, strong endpoint visibility, network monitoring and a focus on identity security all play a role in spotting both the initial infection and the misuse of stolen credentials.

 

Authentication hardening is particularly important. Multi-factor authentication, device-bound credentials and passwordless approaches can significantly limit the damage infostealers can cause, even when credentials are successfully stolen.

Continuous monitoring for unusual behaviour such as logins at odd hours, impossible travel or sudden changes in access patterns can also give security teams the opportunity to respond before stolen data is used to cause serious harm.

 

In the next episode of teissTalk with Thom Langford, we will look more closely at how modern info-stealing malware works, why it is so effective at staying hidden, and what practical, layered defences organisations can put in place to reduce the risk from these quiet but highly damaging threats.