alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE Win32.Sality-GR Checkin 2"; flow:to_server,established; http.uri; content:".png?"; fast_pattern; pcre:"/\.png\x3f[0-9a-f]{4,8}\x3d\d+?$/"; http.header_names; content:!"Accept"; content:!"Referer"; content:"|0d 0a|User-Agent|0d 0a|"; startswith; reference:md5,99d614964eafe83ec4ed1a4537be35b9; classtype:command-and-control; sid:2022804; rev:5; metadata:created_at 2016_05_13, performance_impact Significant, signature_severity Major, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2024_04_29;)