alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET INFO Observed UA-Pixels Header"; flow:established,to_server; http.header_names; content:"|0d 0a|ua-pixels|0d 0a|"; nocase; threshold:type limit, track by_src, seconds 180, count 1; reference:url,oreilly.com/library/view/http-the-definitive/1565925092/re52.html; classtype:misc-activity; sid:2062719; rev:1; metadata:attack_target Client_Endpoint, created_at 2025_06_03, deployment Perimeter, confidence High, signature_severity Informational, updated_at 2025_06_03;)