alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE Lethic - Client Alive"; flow:established,to_server; dsize:6; content:"|01 00 21 01|"; offset:2; depth:4; classtype:trojan-activity; sid:2015522; rev:3; metadata:created_at 2012_07_25, signature_severity Major, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2019_07_26;)