alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET HUNTING robots Request (set)"; flow:established,to_server; flowbits:set,ET.robots; flowbits:noalert; http.method; content:"GET"; http.uri; content:"/robots"; startswith; isdataat:!5,relative; fast_pattern; pcre:"/^(?:\.txt)?$/R"; http.header_names; content:!"User-Agent"; content:!"Referer"; classtype:bad-unknown; sid:2044538; rev:1; metadata:created_at 2023_03_09, confidence Medium, signature_severity Informational, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2023_03_09; target:src_ip;)