A lot of people use a Lockcode/Passcode to stop someone else from accessing their phone. Doing so you feel fairly secure that no one can access you information and use your phone without your approval. Now it seems Siri, the new digital assistant in iPhone 4S, not only assist the owner in different tasks, but also might help total strangers use the phone.
Under the right conditions, Siri will bypass your passcode and allow anyone to perform tasks on a locked phone. By default, you can use Siri to make phone calls, check your calendar, send texts and emails to people in your contacts list, and set reminders, even when your phone is locked with a passcode. But it seems you at least can’t interact with installed applications or do Internet searches. This functionality might be something you prefer, and can be very handy if you for instance want to use Siri while driving your car. The possibility to search from the locked screen can be turned on and off, but the problem is that this functionality is turned on by default.