A keylogger is a surveillance mechanism — implemented as software or hardware — that records every keystroke made on a device. Attackers use keyloggers to capture credentials, financial data, personal messages, and other sensitive input without the user's knowledge.
How It Works
Software keyloggers operate at various levels of the operating system. User-mode keyloggers hook into keyboard input functions within the operating system's event handling. Kernel-mode keyloggers intercept keystrokes at a deeper level, making them harder to detect and remove. Some variants capture clipboard contents, take periodic screenshots, or log application-specific input fields in addition to raw keystrokes.
Distribution methods include phishing emails with malicious attachments, drive-by downloads from compromised websites, bundled software installers, and exploitation of system vulnerabilities. Once installed, the keylogger runs silently in the background and transmits captured data to the attacker via email, FTP, or HTTP requests to a command-and-control server.
Hardware keyloggers are physical devices inserted between a keyboard and computer, typically through a USB or PS/2 connection. They require physical access to install but are invisible to software-based security products. Wireless keyboard sniffers intercept unencrypted radio signals from wireless keyboards, capturing keystrokes without any physical modification to the target system.
Detection and Prevention
Software keyloggers can be detected through behavioral analysis, monitoring for unusual processes that hook into keyboard input, or identifying unexpected network connections. Endpoint protection solutions with behavioral detection capabilities catch many known variants. For hardware keyloggers, physical inspection of keyboard connections is necessary.
Prevention strategies include keeping systems patched, using multi-factor authentication (which limits the value of captured passwords), employing virtual keyboards for highly sensitive input, and maintaining awareness of social engineering tactics that lead to malware installation.
Why It Matters
Keyloggers remain one of the most effective ways to harvest credentials at scale. They bypass encryption entirely by capturing data before it is encrypted, making them a persistent threat to both individuals and organizations. A single compromised set of credentials can lead to full account takeover and lateral movement through an environment.
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