What Is an Infostealer? How It Steals Your Logins

An infostealer is built for collection and resale

Infostealers are a form of spyware whose main job is to gather sensitive data from an endpoint and exfiltrate it. Some run once and disappear; others add persistence or act as a loader for more malware. The operator may use the data directly or sell a “log” containing the victim's device details and captured accounts.

The ESET definition highlights login and bank details. Modern targets go further because the browser has become a concentrated store of identity. Malwarebytes' June 2026 phishing and infostealer analysis describes theft of passwords, cookies, autofill, wallets and files, with several potential buyers for one infected machine.

An infostealer isn't the same as a keylogger, though it may include keylogging. It can read data that already exists on disk or in browser processes without waiting for the victim to type it again.

What an infostealer can take

Why MFA isn't a complete answer

MFA protects the authentication event. A session cookie exists after that event and tells the service that the browser is already signed in. If malware copies a usable token, the attacker may replay the session without entering the password or the same second factor. Services can limit this with short sessions, risk checks and device-bound credentials, but users should still revoke sessions after endpoint compromise.

Phishing-resistant passkeys and hardware security keys remain stronger than SMS or approval prompts. They reduce credential phishing and some account takeover paths; they don't grant immunity to malware executing on the same endpoint.

How infostealers reach normal users

Microsoft's March 2026 fake developer interview report documents malware seeking cloud credentials, signing keys, wallets, password stores and configuration files on both Windows and macOS. It recommends isolated, non-persistent environments for untrusted coding assessments.

Signs are useful, but no symptom is required

• Unexpected login alerts, unfamiliar devices or new active sessions
• Password-reset or MFA messages you didn't initiate
• Unknown email forwarding rules, recovery methods or OAuth applications
• Browser passwords or crypto assets used without an obvious phishing event
• Security tools disabled, exclusions added or suspicious scheduled tasks
• A console or installer flashing briefly after a fake update, CAPTCHA or job task

Many stealers are designed to finish quietly. No slowdown, pop-up or detection doesn't prove the machine is clean. The strongest evidence is often the risky execution event plus account telemetry. If you deliberately ran an unknown file after disabling protection, respond to that fact instead of waiting for a symptom.

Infostealer recovery: contain accounts before normal reuse

1. Take the device offline. Preserve it if a business incident team needs evidence; otherwise stop sensitive use.
2. Use a separate clean device. Secure the primary email and identity-provider account first.
3. Revoke every session. Use “sign out all devices,” remove connected apps and delete unknown app passwords or recovery methods.
4. Change credentials by impact. Password manager, banking, work admin, cloud, crypto and social accounts come before low-value sites.
5. Reset MFA and trusted devices. Add passkeys or security keys after the account is under control.
6. Rotate non-password secrets. API tokens, SSH keys, signing certificates, wallet material and backup codes need their own procedures.
7. Scan outside normal startup. Use Defender Offline or a reputable rescue environment, followed by a second-opinion scan.
8. Reinstall when confidence is low. A clean installation from trusted media restores more confidence than repeated scans after broad compromise.
9. Inspect the aftermath. Review mail rules, cloud logs, financial transactions, ads accounts and developer platforms for misuse.

Recovery isn't complete merely because a product says “threat removed.” Stolen sessions and secrets live outside the machine. The process ends when those paths are revoked or replaced and the endpoint is trusted again.

Practical prevention

• Download software from a known vendor route, not an advertisement or reposted installer.
• Never disable security to run a crack, cheat or unknown “fix.”
• Use a maintained real-time antivirus and keep cloud protection enabled.
• Keep unique passwords in a dedicated manager and lock the vault when idle.
• Use passkeys or FIDO2 keys for primary email, cloud and financial accounts.
• Run untrusted job tasks in a disposable VM with no production credentials.
• Keep recoverable backups that aren't permanently writable from the everyday account.

Our infostealer antivirus comparison maps products to the lure, loader and loot stages. For extension-specific containment, follow the malicious Chrome extension guide.