According to a new Wired report, citing a disclosure by Apple, the data which Apple collects for making improvements to its voice-driven Siri service is anonymized, and is kept on the servers of the company for two years before it is discarded.

The revelation by Apple - that keeps anonymized Siri data for up to two years before discarding it - has come after the company was urged by the privacy advocates to disclose exactly what information it knows about its users and what data it keeps about them.

Elaborating on Apple's practice of discarding anonymized Siri data after retaining it for two years, the company's spokeswoman Trudy Muller said the anonymized data is collected primarily with the aim of bringing about an improvement in the Siri service; and also added that the company considers `customer privacy' to be a very serious matter.

As per the statement by Muller, the turning off of the Siri voice assistant by a user at any time immediately prompts the deletion of the data about that user. In an apparent security measure, Apple does not use the user's Apple ID or email address in its data storage; rather, it assigns a randomly generated number which represents the user and becomes associated with the voice files.

Muller explained to Wired: "Apple may keep anonymised Siri data for up to two years. If a user turns Siri off, both identifiers are deleted immediately along with any associated data."