alert http $EXTERNAL_NET any -> $HOME_NET any (msg:"ET MALWARE Known Sinkhole Response Header"; flow:established,to_client; http.header; content:"X-Sinkhole|3a 20|"; nocase; classtype:trojan-activity; sid:2016803; rev:6; metadata:created_at 2013_05_01, confidence High, signature_severity Minor, updated_at 2020_04_27;)