Your iPhone hasn't been safe for over a month. Thanks to a glitch in iOS 6.1, anyone could bypass the iPhone lock screen by following a series of button presses, leaving the phone completely vulnerable to attack. Apple admitted the exploit on February 14th and has finally released an update to eliminate this bug, more than a month later.
In the upgrade notes, Apple says that iOS 6.1.3 "fixes a bug that could allow someone to bypass the passcode and access the Phone app." The update seems to have rectified the security hole; we attempted to recreate the hack after upgrading an iPhone 4S to the newest version of the operating system but were unsuccessful.
In order to upgrade to iOS 6.1.3, users can attach their iPhones to their notebooks via USB and click "check for updates" in the iTunes application. The new version of the OS can also be installed over air by entering the Settings app, navigating to the "General" tab and then entering the Software Update section.