The Antivirus Web Shell Detection rule is designed to identify malicious artifacts, specifically web shells, that could signify unauthorized access and ongoing compromise on web servers. This rule detects alerts generated by antivirus solutions that indicate the presence of known backdoor signatures associated with various scripting languages such as ASP, PHP, JSP, and others. The rule emphasizes the importance of customizing detection parameters to the signatures employed by the specific antivirus software in use, suggesting users reference comprehensive web shell repositories to fine-tune detection accuracy. Furthermore, despite an antivirus blocking an identified threat, the rule advises investigatory follow-up to comprehend the vectors of entry and potentially remediative measures. It targets high-severity incidents due to the implications of web shell infections in terms of data breaches and system integrity risks.