A shared AMI is an AMI that a developer created and made available for other developers to use. One of the easiest ways to get started with Amazon EC2 is to use a shared AMI that has the components you need and then add custom content.
You use a shared AMI at your own risk. Amazon can't vouch for the integrity or security of AMIs shared by other Amazon EC2 users. Therefore, you should treat shared AMIs as you would any foreign code that you might consider deploying in your own data center and perform the appropriate due diligence.
We recommend that you get an AMI from a trusted source. If you have questions or observations about a shared AMI, use the AWS forums.
Amazon's public images have an aliased owner, which appears as
amazon in the account field. This
enables you to find AMIs from Amazon easily. Other users can't alias their AMIs.