alert tcp $EXTERNAL_NET any -> $HOME_NET any (msg:"MALWARE [PTsecurity] Backdor.W32/Virut"; flow:established, to_client; dsize:68; stream_size:server, <,138; stream_size:client, <,137; flowbits:isset, FB309156_0; flowbits:unset, FB309156_0; threshold:type limit, track by_src, count 1, seconds 30; classtype:trojan-activity; metadata:created_at 2017_7_25; reference:url, github.com/ptresearch/AttackDetection; sid:11001607; rev:2;)