"Apple confirmed that it keeps users' questions for up to two years. Siri, which needs to be connected to the Internet to function, sends all of its users' queries to Apple.
Apple revealed the information after Wired posted an article this week raising the question and highlighting the fact that the privacy statement for Siri wasn't very clear about how long that information is kept or what would be done with it."
http://www.latimes.com/business/technol ... 7017.story