The detection rule 'GCP GCS Ransom Note Upload' identifies the upload of files named after common ransomware notes to Google Cloud Storage (GCS) buckets. Ransomware attackers often leave instructions for payment in files that follow recognizable naming patterns. The rule leverages GCP Audit logs to track such activities, focusing on specific behaviors around file uploads that may indicate malicious intent. The rule entails querying audit logs, checking source IP addresses against known cloud providers or VPNs, and scrutinizing for any changes in Key Management Service (KMS) keys or Identity Access Management (IAM) policies relating to the impacted bucket.