While perhaps a bit unnerving, let's not act like this hasn't happened before. While Apple's engineering team is no doubt massive, there's only so much a fixed group can find. We're talking about bugs in particular; while iOS 7's final build squashed a ton of quirks, a couple of security issues have presented themselves now that the operating system has been unleashed to the masses. In fact, most major companies find themselves in similar spots shortly after a major OS release: users discover exploits, and then, the firm has to work overtime in order to issue a patch (or two) to ensure it doesn't impact the userbase.
The latest iOS 7 bug is one that (in theory) allows anyone to make calls from a locked iPhone. Basically, the exploit involves a bit of trickery within the iPhone's "Emergency Call" function, which is there in the event that someone needed to call 911 even if the SIM wasn't valid. It functions a bit like a brute force attack; you just hop into the Emergency Screen, dial a number, and rapidly press the Call button. If it goes well (or unwell, depending on how you look at it), the call will eventually go through.
Of course, now it's on Apple to issue an iOS point release to patch things up. In the meanwhile, ensure that your iPhone stays by your side... else someone could end up making some pretty strange calls on it without your permission.