What Are Info Stealers?
An info stealer is malware that infiltrates a system, gathers specific categories of sensitive data — credentials, saved passwords, session cookies — and relays them to an attacker. Its value to the criminal is stealth: the theft leaves the machine working normally.
Info stealers frequently operate inside botnets, where an operator issues remote commands to control what the malware collects and when. That centralized control is what turns individual infections into coordinated, large-scale campaigns aimed at specific data or specific users.
- Online banking credentials
- Social media accounts
- Email and recovery inboxes
- FTP and remote access accounts
- Session cookies and auth tokens
- Crypto wallets and payment data
Twenty Years of Credential Theft.
Info stealers did not appear with the AI era. They matured through two decades of iteration — and became a commodity along the way.
ZeuS
A pioneering Trojan built to steal online banking credentials. After its source code leaked, variants multiplied — making it one of the most notorious info stealers ever written.
Koobface
A worm that went after social media credentials, targeting Facebook, MySpace, and Twitter. Credential theft moved beyond banking.
Commodity capability
Info-stealing is no longer a malware family. It is a feature, bundled into botnet agents, keyloggers, droppers, and trojans, and sold as a service.
How Info Stealers Get In.
Distribution follows the same routes as Trojans and botnet agents. None of them require a sophisticated adversary.
Malicious email attachments
Spam campaigns deliver malware-laden attachments at volume. Still the highest-yield route.
Infected websites with exploit kits
A vulnerable site silently downloads and installs the payload. No click required.
Malvertising
Malicious advertisements redirect users to infected sites and initiate the download.
Code repositories
Adversaries increasingly target repositories and development teams — where one theft yields production access.
Info Stealers Rarely Travel Alone.
A stealer is usually one component of a kit. Understanding what accompanies it explains why a single detection rarely ends the incident.
Downloaders / Trojan droppers
Pull additional payloads down, including the stealer itself.
Botnets
Networks of infected machines under a command-and-control server, enabling coordinated, remotely tasked theft.
Keyloggers
Track and record keystrokes, feeding credential capture.
Types of Infostealer Malware
Some common types of infostealer malware include the categories mapped below — each defined by what it targets and how it captures it.
7 Critical Defense Strategies.
Ordered by leverage. The first three remove the attacker’s payoff and their ability to execute; the rest contain what gets through and shorten your recovery.
01 Make the stolen credential worthless Phishing-resistant MFA and passkeys +
A password harvested from a browser vault is only valuable if it is sufficient to log in. Move to hardware-backed passkeys or FIDO2 for every account that matters. SMS and app codes are better than nothing, but they are replayable — a stealer that captures a live session does not need the second factor at all.
02 Stop trusting the browser as a password vault Remove the saved-credential surface +
Saved passwords and autofill entries are the single richest target on a compromised endpoint, and they are readable with user-level permissions. Move secrets into a dedicated manager, disable browser credential storage by policy, and clear what is already there.
03 Deny execution by default Application control, not detection +
An info stealer must run to steal. Signature and behavioral detection asks whether a process looks malicious; default-deny asks whether it was authorized. Only the second question has a deterministic answer. Allow-list what belongs on the endpoint and block everything else at the kernel boundary.
04 Assume the session is stolen, not just the password Short-lived tokens and revocation +
Session cookies let an attacker bypass authentication entirely. Shorten token lifetimes, bind sessions to device posture, and make revocation a one-click operation your help desk can actually perform mid-incident.
05 Harden the developer path Repositories, pipelines, and build agents +
Adversaries target code repositories and development teams because one stolen developer identity yields signing keys, pipeline access, and production credentials at once. Treat developer endpoints as production systems, enforce commit signing, and scope CI secrets to single jobs.
06 Watch for your credentials in the wild Stealer-log and exposure monitoring +
Harvested credentials are resold in bulk before they are used. Monitoring exposure feeds for your domains, converts a future breach into a present-day password reset — the only point in the chain where you get ahead of the attacker.
07 Rehearse the credential-theft recovery A playbook, not an intention +
When a stealer log surfaces, the clock is measured in hours. Decide in advance who force-resets, who revokes sessions, how you reach the affected user, and what evidence you preserve. An untested plan is an assumption.
An Info Stealer Has to Run Before It Can Steal.
That single fact decides which control works. Every detection product evaluates a process that is already executing, using indicators derived from malware that has already been seen. Stealers are repackaged continuously to defeat exactly that, and the theft itself uses legitimate operating-system functionality.
“Does this process look malicious?”
A probabilistic question, answered after execution begins, against an adversary who rebuilds the binary daily.
“Was this authorized to execute?”
A deterministic question, answered before execution, and unaffected by how novel the payload is.
You cannot detect your way out of a threat that is redesigned faster than signatures ship.
Info Stealers, Answered.
What is an info stealer?+
An info stealer is malware designed to collect sensitive data from an infected computer and relay it back to an attacker. It typically targets credentials for online banking, email, social media, and remote-access accounts, along with saved passwords and live session cookies.
How do info stealers actually capture credentials?+
Five techniques dominate: hooking the browser to capture credentials as they are typed, injecting scripts that modify web forms, grabbing form content from specific open windows, logging keystrokes, and extracting saved passwords and cookies already stored by the browser or operating system.
How does an info stealer get onto a machine?+
Primarily through the same routes as Trojans and botnet agents: malicious email attachments, compromised websites running exploit kits, malvertising that redirects to infected sites, and increasingly, poisoned code repositories aimed at development teams.
Does antivirus stop info stealers?+
Not reliably. Stealers are built for stealth and are repackaged constantly to defeat signatures, and the theft itself uses legitimate system functionality. Detection identifies known-bad behavior after execution begins. Preventing unauthorized execution in the first place is the control that holds.
If a stealer only took saved passwords, is changing them enough?+
No. Modern stealers take session cookies alongside passwords, and a valid session token bypasses both the password and multi-factor authentication. Credential rotation must be paired with session revocation across every affected service.
What is a stealer log?+
A packaged dump of everything harvested from one infected machine — credentials, cookies, autofill data, system details — sold or traded in bulk. Most account takeovers begin with someone buying a log, not with the original infection.
Which malware families are known for this?+
ZeuS is the archetype, targeting banking credentials from 2006 onward. Tinba is a lightweight financial stealer, CoreBot is modular and adaptable, and the Neutrino botnet is known for distributing stealers among other payloads. Today the capability is bundled into most commodity malware.
The Credential Is Already Stolen. The Question Is Whether It Works.
Assume a stealer log with your domain in it exists. Passkeys, default-deny execution, and fast session revocation are what make that log worthless.
Deny the execution. Devalue the credential. Shorten the session.