This unique vulnerability was picked up by researchers at Texas University in Austin, and taking into consideration just how widespread Android Lollipop has made its way around in the Android ecosystem, it potentially affects 21% of Android devices that are currently in use, where all that the attacker needs to do to is to overload the lock screen with text, nothing else.
Do bear in mind that if your Android Lollipop-powered handset has been set to PIN or pattern unlock, it will remain safe and sound. This is an attack that requires physical access to the handset, and a software update should be able to squash the bug nice and good.