You can’t rely on a monitor privacy film to prevent other users from seeing what you type. If your computer is infected with a keylogger, the hacker who deployed it will capture your keystrokes. Also known as keyboard-capturing malware, keyloggers are a form of malware that record keystrokes. They will record each letter, number and special character that you type. Here are six things that you probably didn’t know about keyloggers.

#1) Hard to Detect

Antivirus software isn’t enough to protect against keyloggers. Research shows that 80% of keyloggers are not detachable by antivirus software. They are able to conceal themselves on users’ computers — all while recording the users’ keystrokes. Whether it’s a quick scan or a full-system scan, antivirus software may not detect keyloggers.

#2) Legitimate Purposes

When most people think of keyloggers, they envision keystroke-logging malware. Some keyloggers, however, are used for legitimate purposes. Businesses, for instance, may use them to oversee their employees’ typing. Remote workers may use them for similar legitimate purposes. When used for a legitimate purpose, keyloggers aren’t classified as malware.

#3) Hardware vs Software Based

Some keyloggers are hardware based, whereas others are software based. Hardware-based keyloggers leverage a device, such as a Universal Serial Bus (USB) flash drive. The malicious USB flash drive must be installed in a computer in order for the keylogger to infect the computer. Software-based keyloggers, on the other hand, are entirely digital. They consist of malicious code that’s deployed on a computer or network.

#4) Keyboard Clipping

While their primary function is to record keystrokes, keystrokes may exhibit other characteristics. Some of them support keyboard clipping. When you clip a string of text to your computer’s keyboard, the keylogger will record it. You don’t have to necessarily type the text. Simply copying the text to your computer’s keyboard will compromise the text via this keylogger feature.

#5) Screenshot Capturing

In addition to keyboard clipping, some keyloggers support screenshot capturing. Screenshot capturing is exactly what it sounds like: a keylogger feature that involves taking a screenshot of your monitor. If you type a password or other sensitive information, the hacker behind the keylogger may see it. Of course, this is why most websites and software products black out password fields: to prevent unauthorized users from seeing the password.

#6) Anti-Keyloggers

Antivirus software may prove ineffective at detecting keyloggers, but fortunately there are anti-keyloggers. Anti-keyloggers consist of security software products that are designed to detect and eliminate keyloggers. Keyloggers often have “footprints.” An anti-keylogger will check for these signatures to determine whether your computer is infected with a keylogger.