Increasingly, new services created by the likes of Apple, Google, and others offer convenient mobile tools that help us organize our lives, from business matters to personal connections. However, those same services often require that personal data is collected, analyzed, and stored.

As a result, some groups have raised questions as to how long this private data is kept, and one of the services under review is Apple's Siri.

Amidst inquiries from the American Civil Liberties Union, an Apple spokeswoman told Wired that Apple keeps "anonymized Siri data for up to two years, [and] if a user turns Siri off, both identifiers are deleted immediately along with any associated data."

The ACLU has tackled this issue in the past, but the issue re-emerged this week after an exchange between Nicole Ozer, a lawyer with the ACLU, and Wired.

According to Apple's Siri privacy policy, "if you turn off Siri, Apple will delete your User Data, as well as your recent voice input data. Older voice input data that has been disassociated from you may be retained for a period of time to generally improve Siri and other Apple products and services."

That document, however, does not appear to be posted on Apple's website, so this is reportedly the first time Apple has revealed how long it keeps data sent into Siri. Ozer told Wired that "there is no good reason for Apple to not include information about privacy practices on their Siri FAQ page."

As of this writing, Apple's Siri Frequently Asked Questions page and general privacy policy page do no reflect the length of time the system holds onto user data.

Data retention has made headlines in recent years, from Internet companies like Yahoo, Microsoft, and Google to wireless providers like AT&T and Verizon.

In 2011, the ACLU filed a Freedom of Information Act (FOIA) request related to an investigation into cell phone location tracking by police. Ultimately, the ACLU of North Carolina obtained the cell phone data retention document, and it was revealed that carriers keep data up to seven years, depending on your provider.

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