Apple is waving the victory banner over the tremendous amount of users who have upgraded their devices to iOS7 or have bought the new iPhone 5c and 5s with iOS7. Truly they have achieved success, but because of that success, they are the target of those who would hack and compromise the security of their devices and software.
Application security vendor, Cenzic, has discovered a flaw that allows a person to access a locked device without the password using Siri to send Facebook messages posing as the device owner. They have also been able to text, e-mail, and access contacts. The flaws also exist in iOS6, but apparently to a more limited extent. They recommend disabling Siri until Apple fixes the compromised code.
Read more about this from: Dark Reading article