Final answer:
Fileless viruses store themselves in the RAM to avoid detection and maintain persistence, exploiting system tools to run malicious activities while leaving no traces on the hard disk after reboot.
Step-by-step explanation:
Fileless viruses often store themselves in the Random Access Memory (RAM) to maintain persistence. Unlike traditional malware, which writes data to the hard disk drive, fileless malware resides in the volatile memory of a computer. This tactic enables the malware to evade many antivirus detection methods because it does not leave easily detectable traces on the hard drive. By living in the RAM, the fileless virus can run its malicious activities as long as the computer is on, but its footprint disappears when the machine is rebooted, making it more challenging to detect and remove. Fileless viruses exploit applications and Windows management tools, such as PowerShell or WMI, to execute malicious code directly in memory.