The JPS Virus Maker 4.0 is a software tool that allows users to create and customize their own viruses, Trojans, and other types of malware. The tool is designed to be user-friendly, with a simple interface that guides users through the process of creating a malicious program. The software claims to be able to create viruses that can evade detection by antivirus software and can even be used to create "undetectable" malware.