alert tcp $EXTERNAL_NET 443 -> $HOME_NET any (msg:"ET MALWARE STARSYPOUND Client Checkin"; flow:established,from_server; content:"*(SY)# "; depth:7; reference:md5,8442ae37b91f279a9f06de4c60b286a3; reference:url,www.mandiant.com/apt1; classtype:command-and-control; sid:2016444; rev:3; metadata:created_at 2013_02_20, signature_severity Major, updated_at 2019_07_26;)