Does anyone know if it's possible to set your profile so it doesn't show whether you are live online or not.

Whenever I come on italki I get live messages from guys who haven't filled anything in on their profile and with no posted community contributions or friends. It's not like they're introducing themselves or anything - they just say hi... or hello... and nothing else. To be honest it feels a bit creepy (I know it's probably not meant that way) and I'd rather it didn't happen.

So... can anybody tell me how to set my status as invisible/unknown?