It's no secret that Apple hangs onto your Siri data for some length of time (as other companies so with search data and the like), but it hasn't been clear exactly how long it keeps that data sitting on its servers. Wired has now cleared that up somewhat, though, hearing from Apple spokesperson Trudy Muller that the company "may keep anonymized Siri data for up to two years." That word follows another report from Wired yesterday that raised concerns about the issue. As Muller notes, the data is immediately deleted if a user turns Siri off at any time, and it's anonymized from the start; neither your Apple ID or email address are stored with a data, but rather a randomly generated number that represents the user and becomes associated with the voice files. That number then gets disassociated from voice clips after six months, but Apple still hangs onto the files for another 18 months for what's described as testing and product improvement purposes.
Update: The Financial Times has confirmed with Google that it, too, keeps your voice search data for up to two years. Google itself has previously detailed how it handles that data, including the added measures put in place when a user opts-in for personalized voice recognition; in that case, electronic keys linked to your account are generated that Google says are "designed to be accessed by machines, not people."