alert tcp $EXTERNAL_NET any -> $HOME_NET any (msg:"ET MALWARE ELF/Emptiness v1 DNS Flood Command Inbound"; flow:established,from_server; content:".dns|20|"; depth:5; fast_pattern; pcre:"/^((\d{1,3}\.){3}\d{1,3}|((?:https?\x3a\/\/)?[a-z0-9\-]{1,30}\.){1,8}[a-z]{1,8})/Ri"; reference:url,blog.netlab.360.com/emptiness-a-new-evolving-botnet/; classtype:trojan-activity; sid:2027838; rev:1; metadata:affected_product Linux, created_at 2019_08_09, malware_family Emptiness, confidence High, signature_severity Major, tag DDoS, updated_at 2019_08_09;)