alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE Arid Viper APT Possible User-Agent (Skype)"; flow:established,to_server; http.header; content:"|0d 0a|REMOTE_USER|3a 20|"; http.user_agent; content:"Skype"; nocase; fast_pattern; bsize:5; http.header_names; content:!"Referer|0d 0a|"; reference:url,trendmicro.com/cloud-content/us/pdfs/security-intelligence/white-papers/wp-operation-arid-viper.pdf; classtype:targeted-activity; sid:2020442; rev:4; metadata:created_at 2015_02_17, confidence Medium, signature_severity Major, updated_at 2020_09_29;)