What type of software collects every keystroke entered on a computer?

The type of software that collects every keystroke entered on a computer is known as a key logger. This software is specifically designed to monitor and capture keyboard input, which can include everything from usernames and passwords to other sensitive information. Key loggers can be utilized for various purposes, such as ethical hacking and monitoring employee activity. However, they are often associated with malicious intent when used without consent, as they can invade privacy and facilitate identity theft.

In this context, the other options do not serve this function. Adware typically serves to display unwanted advertisements and can track browsing habits but does not specifically capture keystrokes. Data backup software is intended for creating copies of data to prevent loss, while firewall software focuses on controlling incoming and outgoing network traffic for security purposes. None of these tools are designed to log keystrokes, highlighting why the key logger is the correct choice.