alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE Linux/Xnote Keep-Alive"; flow:established,to_server; dsize:17; content:"|11 00 00 00 01 00 00 00 78 9c 4b 05 00 00 66 00 66|"; fast_pattern; reference:url,deependresearch.org/2015/02/linuxbackdoorxnote1-indicators.html; classtype:trojan-activity; sid:2020389; rev:2; metadata:created_at 2015_02_11, confidence High, signature_severity Major, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2019_10_08;)