What is a Remote Access Trojan (RAT)?

A Remote Access Trojan (RAT) is a malicious software program that allows an attacker to take control of a computer remotely. It is typically installed without the user's knowledge and gives the attacker persistent access to the infected system. This access enables the attacker to perform a variety of malicious activities such as stealing sensitive information, spying on users through webcams, capturing keystrokes, and more. The RAT operates in stealth mode, often evading detection by traditional security systems, and allows for not only remote access but also control over the targeted system.

The other options describe concepts that do not align with the nature of a RAT. While securing remote connections is important, a RAT is specifically a tool used by attackers and does not serve a legitimate purpose or provide security. Antivirus software is designed to detect and remove viruses and malware, which is the opposite of what a RAT does. Lastly, while there are legitimate remote access programs, a RAT is classified as malicious because it is deployed for harmful purposes, rather than as a trusted tool. Thus, the definition that identifies it as an attacker-controlled tool for persistent access is accurate and encompasses the core characteristics of a Remote Access Trojan.