Keystroke Loggers, or keyloggers, are tools – software or hardware – that record the keys a user presses on a keyboard, capturing everything they type: usernames, passwords, messages, credit card numbers, and other sensitive information. In a malicious context, keyloggers are a form of surveillance used by attackers to secretly harvest credentials and confidential data directly as the victim enters it, before that data is encrypted or protected by the application. They are a classic and enduring tool of credential theft and espionage.
Keyloggers come in two broad forms. Software keyloggers are programs installed on a victim’s device, often delivered as part of malware or a trojan through phishing, malicious downloads, or exploited vulnerabilities. They run stealthily in the background, logging keystrokes (and sometimes also capturing screenshots, clipboard contents, and other activity) and transmitting the collected data back to the attacker. Hardware keyloggers are physical devices – for example, a small connector placed between a keyboard and computer, or a compromised keyboard – that record keystrokes at the hardware level; these require physical access to install but can be very difficult to detect through software means.
The danger of keyloggers is that they capture data at the point of entry, bypassing many downstream protections. Even if a website uses encryption in transit, the keylogger records the password as the user types it, before it ever leaves the device. This makes keyloggers highly effective for stealing credentials, which then feed account takeover, fraud, and deeper compromise. Because they operate silently, victims often have no indication their keystrokes are being captured.
Keyloggers relate to broader security concerns because the credentials they steal are the raw material for credential abuse, account takeover, and unauthorized access to systems and APIs. A single infected endpoint can leak the credentials that unlock many accounts.
Defending against keyloggers involves several layers: endpoint protection and anti-malware to detect and block keylogging software, keeping systems patched to prevent the exploits that deliver them, user awareness to avoid phishing and malicious downloads, and physical security to prevent hardware keyloggers. Multi-factor authentication is an important mitigation for the consequences, because even if a password is captured, the additional authentication factor can prevent the attacker from using it. Monitoring for the anomalous account activity that follows credential theft also helps catch abuse enabled by keyloggers.