Under the AWS shared responsibility model, AWS is responsible for ensuring the security of the internal network in the AWS data centers, as well as the physical security of the hardware and facilities that run AWS services. AWS customers are responsible for configuring the security group rules that determine which ports are open on an EC2 Linux instance, patching the guest operating system with the latest security patches on EC2, and turning on server-side encryption for S3 buckets. Source: AWS Shared Responsibility Model