Amazon employs thousands of employees around the world to help improve the work of its Echo and Alexa digital assistants.

A recent report by Bloomberg reported that a number of these staff were listening to voice recordings by customers at their homes or offices with Echo.

It was believed that these conversations, usually conducted through the system of voice recognition in the device are protected and respond to them through an automated system without human intervention to protect privacy.

"We take the security and privacy of our customers' personal information very seriously," an Amazon spokesman told Bloomberg. "We only take a very small sample of customer registrations to improve their experience with the PDA."

But Bloomberg points to a large workforce doing this kind of work, saying Amazon has employees listening to audios in offices in Boston, Costa Rica, India and Romania. The number of syllables they listen to may be 1,000 in a nine-hour shift.

Amazon needs to listen to client segments rather than machines; it needs to train program algorithms to respond more closely to humans than machines, which staff provide when reviewing these sections and making notes for subsequent entry into the system.

But why is not Amazon more explicit about the role of human reviewers in its published policy?

On Amazon's Privacy Policy and FAQs page, "We use your requests to Alexa to train speech recognition systems and understand our natural language" without mentioning the human element.

Amazon told Bloomberg that it had strict privacy safeguards to prevent abuse of the system. "Employees do not have direct access to information that can identify a person or account as part of the workflow," the company spokesman said. "All information is treated with high confidentiality and we use multi-factor authentication to restrict access, encrypt the service and review our control environment to protect it."

Staff sometimes hear a loud or unexpected sound, according to Bloomberg reports. In one case, two workers heard what appeared to be potential sexual assault, but were told that the intervention was inappropriate.

Staff can discuss what they hear with other internal chat staff, and can share clips they have difficulty interpreting, although the report also states that the files are simply shared because they are "amusing".

The Bloomberg report says Apple and Google have human references.