The company has never accepted it, which has given rise to several business models, including Purse.io and Moon's recent browser extension.

AMAZON FINALLY SEEING THE LIGHT FOR DDOS PREVENTION
Amazon has reportedly filed for a patent involving cryptographic proof-of-work, the system that underpins Bitcoin and most major cryptocurrencies. Proof-of-work is a concept invented by Adam Back as part of hashcash, primarily as a means to make it very expensive to conduct denial-of-service attacks.

Amazon mentions this in the earlier paragraphs of its patent application:

"Computer networks have evolved to provide sophisticated functionality in a large variety of contexts. Providing such functionality, however, often involves complex systems that malicious entities may try to exploit. One such attack involves denial-of-service attacks, which can be disruptive to computer systems on a network. In a distributed denial-of-service attack, for instance, large numbers of requests are sent to a computer system to attempt to overload the computer system. One way to mitigate against such attacks is to configure a service such that requests to the service incur some sort of expense, thereby providing disincentive to participating in the attack. One such expense involves imposing a condition that a client submitting a request expend more computational resources (e.g., CPU cycles) to cause the request to be fulfilled."