The 'Virtual Machine Fingerprinting via Grep' rule is designed to detect adversarial behaviors where non-root users attempt to gather detailed information about a system’s operating environment and hardware, specifically targeting virtual machines. This rule identifies the use of common commands such as 'grep' and 'egrep' with specific arguments that are indicative of virtual machine detection (e.g., identifiers for Parallels, VMware, or VirtualBox). It notes that this behavior has been observed in various malware, including Pupy RAT. The detection is sensitive to commands executed by users other than the root. False positives may occur from legitimate usage of these commands, necessitating the ability to whitelist certain users or processes to reduce noise in alerts. The rule includes extensive guidance for triage, potential false positive cases, and recommended response actions. Users should pay attention to the command-line arguments and the context of their execution to assess potential security incidents.