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;)