Amazon.com has revealed it fell victim to “extensive” fraud for six months last year, with hackers stealing funds from several merchant accounts.

According to Bloomberg, the serious online attack saw hackers infiltrate around 100 Amazon seller accounts and loan pools, funnelling funds into their own bank accounts.

Amazon reportedly issued over $1 billion in loans to merchants last year, however, it’s unclear how much hackers stole.

Legal documents claim the hack occurred between May – October 2018.

A spokesperson affirms Amazon has finished investigating the incident, with phishing techniques potentially used to capture confidential information from sellers.

Hackers are said to have changed account details on its Seller Central platform to their own at Barclays Plc and Prepay Technologies (partly owned by Mastercard).

Legal filings reportedly do not disclose how hackers were able to add additional bank details to merchant accounts.

Several commentators have slammed Amazon over the vulnerabilities, with the world’s biggest e-commerce seller focused on automation and minimal human input.