What type of software is designed to be installed secretly and control a computer?

The correct answer is spyware, which is a type of malicious software specifically designed to infiltrate a computer system without the user's knowledge. Once installed, spyware can collect various types of data, including personal information, browsing habits, and even login credentials. It operates stealthily in the background, often bundled with legitimate software or downloaded inadvertently by users.

Spyware can pose significant privacy and security risks as it may transmit the collected data to external parties, thus compromising sensitive information. Recognizing the characteristics of spyware is essential for users to implement necessary precautions, such as using antivirus software and maintaining cautious online habits to mitigate these threats.

Other options do not fit the description of being secretly installed to control a computer. Adware displays advertisements and may track browsing habits, but it is not designed primarily to control a computer. Spam refers to unsolicited email messages, not software that controls systems. A firewall serves as a security measure to prevent unauthorized access but does not involve covert operations or monitoring.