What Exactly Is a Stealer Log?

A stealer log is not just a file – it's the full memory of a stolen identity. It's a structured package created by infostealer malware that collects everything a user's device "knows": browser-saved passwords, session cookies, autofill data, cryptocurrency wallet keys, FTP/VPN credentials, even system fingerprints and chat tokens.

These logs are then uploaded to command-and-control (C2) servers, sorted, and sold in underground markets or Underground Clouds of Logs (UCLs) - massive searchable databases where criminals can look up victims by country, company domain, or even application type.

Kaspersky's 2025 Data Stealer Storm analysis notes that by 2023, over 16 million unique infections had produced harvestable logs. The number is projected to reach 20-25 million in 2024, signaling an epidemic scale of credential theft.

Why Stealer Logs Are So Dangerous?

Unlike ransomware, stealers don't make noise - they simply take everything silently. The real danger lies in persistence: data once stolen remains valuable for months or years.

Credential Reuse: Verizon DBIR 2025 found that 88 % of web-application breaches involved stolen credentials. Attackers reuse these in "credential-stuffing" attacks against corporate SSO portals, cloud services, and developer tools.

Session Hijacking: Stolen cookies can bypass MFA - an attacker can import a valid session and impersonate the user instantly.

Corporate Spillover: Logs often contain both personal and work accounts, allowing attackers to pivot from personal Gmail or Discord tokens to enterprise assets.

Financial & Reputational Damage: Kaspersky observed that one in every 14 infostealer incidents included credit-card data, illustrating direct monetary loss potential.

How Stealer Logs Are Born - the Infection Pipeline

This streamlined process means attackers can produce thousands of logs per hour, automatically tagged with country, domain, and timestamp.

Underground Clouds of Logs (UCLs): The Industrialization of Theft

In 2025, cybercriminals don't need to hack companies manually - they query databases of existing victims. A UCL acts like Google for stolen data: an attacker can search "@company.com" or "VPN credentials" and instantly buy relevant logs. Subscription access models (daily, weekly, VIP) have turned stolen credentials into a SaaS-like ecosystem. This commoditization accelerates the cycle: once one actor steals, hundreds can exploit.

Recent Trends and Observations

Rise of new families: Kaspersky lists RedLine ( 34 %), RisePro (22 %), Lumma (21 %) and Stealc (13 %) as the most active infostealers of 2024.

Target domains: .gov, .edu, and .com TLDs with weak MFA remain preferred; attackers filter for corporate domains with saved sessions.

Delivery evolution: Fake browser updates and AI-tool installers dominate current malvertising campaigns.

Geographic focus: The 2025 data shows strong activity in Europe, MENA, and LATAM - regions with large SMB digitalization and less mature detection stacks.

The Human Factor & Hybrid Devices

Remote work has blurred the line between personal and professional devices. Logs from a single infected laptop often contain credentials from personal e-commerce accounts and corporate VPNs side by side. This "credential hybridization" fuels third-party breaches and supply-chain compromise.

Defensive Playbook