AppleInsider writes today that Ars Technica’s Jacqui Chen has reported on the discovery of a second vulnerability affecting a user’s lockscreen in iOS 6.1. This is, apparently, similar to the other vulnerability that was found recently, but this one can also make your phone’s screen go black, and will enable the hacker using the exploit to plug the phone into a computer and access your data. Also as with the previous exploit, all the hacker has to do is get hold of your phone, then make an emergency call on an iOS device that has been passcode locked, and then immediately cancel it. So, essentially, what this means is that once someone gets your iPhone or iPad, just because you have passcode-locked it, it doesn’t mean that your data, such as your contacts and voicemails, is safe. As AppleInsider notes, a fix for the previous bug is currently in the works from Apple, so that will possibly be updated before release to deal with this new bug.
Source: Another lockscreen passcode flaw found in Apple's iOS 6.1