Blargh:

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"ETPRO TROJAN Babylon RAT Checkin 1"; flow:established,to_server; dsize:<4; content:"|ba ff af ff|"; fast_pattern; threshold:type limit, seconds 30, count 1, track by_src; metadata: former_category TROJAN; reference:md5,8307b99011d009a34c9eebbfcdc3d01c; classtype:trojan-activity; sid:XXXXXXX; rev:1; metadata:affected_product Windows_XP_Vista_7_8_10_Server_32_64_Bit, attack_target Client_Endpoint, deployment Perimeter, tag RAT, signature_severity Major, created_at 2018_06_30, malware_family Remcos, performance_impact Low, updated_at 2018_06_30;)