alert tcp $EXTERNAL_NET any -> $HOME_NET any (msg:"MALWARE [PTsecurity] Backdor.W32/Virut pkt checker #2"; flow:established, to_client; dsize:300<>400; stream_size:server, <,409; stream_size:client, <,82; flowbits:isset, FB303766_1; flowbits:unset, FB303766_1; flowbits:set, FB303766_2; flowbits:noalert; threshold:type limit, track by_src, count 1, seconds 30; classtype:trojan-activity; metadata:created_at 2017_7_17; reference:url, github.com/ptresearch/AttackDetection; sid:11002263; rev:1;)