Strange keyhole icon in status Bar?

[AC Question]

Hi, I have a slightly older set up. A samsung GT9082 (galaxy grand duos) on 4.1.2. This evening a weird new status icon appeared and Ive spent 2 hours searching the net to find out what it is, it look like a simple keyhole? can someone put me out of my misery? What the hell is it!! pic of phone status bar below, its the one on left as you look at it. thx

tinypic.com/r/oic8d4/9