A keylogger is a type of system monitor that has the ability to record all keystrokes on your computer. Therefore, a keylogger may monitor keystrokes, e-mails, chat room dialogue, instant message dialogue, Web sites visited, usernames, passwords, programs run, and any other typed material. They may have the ability to run in the background, hiding their presence. Keyloggers and system monitors may be used for legitimate purposes but can also be installed by a user to record sensitive information for malicious purposes.

Someone with administrative access to your computer, such as a system administrator or someone who shares your computer, typically installs commercial system monitors. This program may be installed on the machine without your knowledge or consent, and may allow an unauthorized, third party to view potentially sensitive information.

Worst case scenario: A third party may be able to view your personal conversations and may gain access to private information such as your usernames, passwords, credit card numbers, or your Social Security number.