alert http $EXTERNAL_NET any -> $HOME_NET any (msg:"ET MALWARE Known Sinkhole Response Header"; flow:established,to_client; http.header; content:"Server|3a 20|malware-sinkhole"; nocase; classtype:trojan-activity; sid:2033105; rev:1; metadata:attack_target Client_Endpoint, created_at 2021_06_07, deployment Perimeter, confidence High, signature_severity Minor, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2021_06_07;)