alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE Backdoor.Win32.Prosti Checkin"; flow:from_client,established; content:"&first& # 0d 0h "; depth:16; reference:md5,5113c6dbd644874482f3a26650970600; classtype:command-and-control; sid:2013769; rev:1; metadata:created_at 2011_10_12, signature_severity Major, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2019_07_26;)