Infostealers are malware designed to collect valuable information from a device: saved passwords, browser cookies, session tokens, cryptocurrency wallets, autofill data, files, screenshots, and system details. Their danger is speed. Stolen data can be sold or used before a victim realizes the device is infected.
How they arrive
Common delivery includes cracked software, fake browser updates, malicious advertisements, game modifications, fraudulent AI tools, email attachments, search-engine advertisements, and compromised websites. The installer often looks useful and may run the expected program alongside the malware.
Why cookies matter
A session cookie may let an attacker reuse a logged-in browser session without knowing the password. MFA protected the original login, but the token represents the result. High-value targets include email, cloud consoles, developer platforms, business applications, and social accounts.
Warning signs
Unexpected account sessions, security alerts, cryptocurrency transfers, new inbox rules, messages sent from your accounts, disabled protections, suspicious downloads, and sudden browser changes deserve investigation. Many infections remain quiet, so absence of symptoms is not proof of safety.
Response priorities
Disconnect the suspected device when active theft is plausible. For work equipment, contact security immediately. From a known-clean device, secure email and the password manager first, revoke sessions and tokens, rotate exposed credentials, and review MFA and recovery settings.
Reinstalling or reimaging is often safer than assuming one detected file was the whole infection. Restore only trusted data and correct the delivery path. Treat credentials stored or used on the device during the exposure window as potentially compromised.
Prevention
Install software from trusted sources, block ordinary users from unnecessary administration, keep browsers and systems updated, limit extensions, use endpoint protection, filter risky downloads, and monitor identity activity. Passkeys reduce reusable password theft but do not make an infected unlocked endpoint harmless.
The bottom line
Infostealers turn one endpoint compromise into many identity compromises. Respond across both layers: rebuild trust in the device and invalidate everything the device may have revealed.
