To streamline their operations, many sellers rely on specialized business apps that tap into the Amazon Marketplace Web Service APIs, which can integrate data including sensitive customer information like names, emails, and delivery addresses.

A new report from threat detection firm RiskIQ details how Magecart hackers have found a way to scan Amazon S3 buckets—cloud repositories that hold data and and other backend necessities for sites and companies—for any that are misconfigured to allow anyone with an Amazon Web Services account to not just read their contents, but write to them, implementing whatever changes they want.

For example, the cloud monitoring and defense firm RedLock said in February that Tesla's Amazon Web Services cloud infrastructure was running mining malware thanks to an inconspicuous, but extensive cryptojacking campaign.