alert http $EXTERNAL_NET any -> $HOME_NET any (msg:"ET SCAN Nessus User Agent"; flow:established,to_server; threshold:type limit, track by_src,count 1, seconds 60; http.user_agent; content:"Nessus"; nocase; depth:40; reference:url,www.nessus.org; classtype:attempted-recon; sid:2002664; rev:11; metadata:created_at 2010_07_30, confidence High, signature_severity Informational, updated_at 2020_04_22;)