ET MALWARE Click Fraud Checkin

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"ET MALWARE Click Fraud Checkin";
    flow:to_server,established;
    http.method;
    content:"GET"; nocase;
    http.uri;
    content:"/link.txt?"; fast_pattern;
    pcre:"/^\/link\.txt\?[0-9]{1,2}\x3a[0-9]{1,2}\x3a[0-9]{1,2}/";
    http.user_agent;
    content:"Mozilla/3.0 (compatible|3b 20|Indy Library)";
    classtype:command-and-control;
    sid:2023669; rev:4;
    metadata:affected_product Windows_XP_Vista_7_8_10_Server_32_64_Bit, attack_target Client_Endpoint, created_at 2016_12_19, deployment Perimeter, malware_family Maldoc, performance_impact Low, confidence High, signature_severity Major, updated_at 2020_10_07;
)