ET MALWARE Powershell commands sent when remote host claims to send an image

alert http $EXTERNAL_NET any -> $HOME_NET any (
    msg:"ET MALWARE Powershell commands sent when remote host claims to send an image";
    flow:established,from_server;
    http.content_type;
    content:"image/jpeg"; startswith;
    file.data;
    content:"New-Object"; nocase;
    content:"System.Net.WebClient"; nocase;
    content:"Start-Process"; fast_pattern;
    classtype:trojan-activity;
    sid:2025007; rev:5;
    metadata:affected_product Windows_XP_Vista_7_8_10_Server_32_64_Bit, attack_target Client_Endpoint, created_at 2017_11_16, deployment Perimeter, malware_family PowerShell_Downloader, performance_impact Low, confidence High, signature_severity Major, updated_at 2020_11_05;
)