alert http $EXTERNAL_NET any -> $HOME_NET any (msg:"ET MALWARE Known Sinkhole Response Header"; flow:established,from_server; http.header; content:"X-Sinkholed-Domain|3a|"; reference:md5,723a90462a417337355138cc6aba2290; classtype:trojan-activity; sid:2017662; rev:4; metadata:created_at 2013_11_04, confidence High, signature_severity Minor, updated_at 2020_04_29;)