alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE W32/ZxShell Checkin"; flow:established,from_server; dsize:16; content:"|86 19 00 00 04 01 00 00|"; depth:8; reference:url,blogs.cisco.com/talos/opening-zxshell/; classtype:command-and-control; sid:2019588; rev:1; metadata:created_at 2014_10_29, confidence Medium, signature_severity Major, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2019_07_26;)