alert smtp $HOME_NET any -> $EXTERNAL_NET [25,587] (msg:"ET MALWARE Hawkeye Keylogger SMTP Beacon"; flow:established,to_server; content:"Subject|3a 20|"; content:"SGF3a0V5ZSBLZXlsb2dnZXIg"; within:45; reference:md5,dfc2c23663122ac9fc25b708f278c147; classtype:trojan-activity; sid:2021871; rev:3; metadata:attack_target Client_Endpoint, created_at 2015_09_30, deployment Perimeter, signature_severity Major, tag c2, updated_at 2019_07_26, mitre_tactic_id TA0010, mitre_tactic_name Exfiltration, mitre_technique_id T1041, mitre_technique_name Exfiltration_Over_C2_Channel;)