This is a few weeks ago now, and I simply removed it, but it's been bugging me since. I have since performed a factory reset, as I was worried about some other issues, and it was the straw that broke the camels back.
It appeared out of nowhere, and I had not recently upgraded or used the Find My Mac feature, which I understand can trigger it. It had three boxes checked 'mail', 'safari' and 'cloud'. My firewall was on, stealth mode active, all sharing denied. Could someone somehow have gotten into my system and set it up remotely? There's no possibility of a hand's on set up.
I checked everything I could think of and just can't see how it could have appeared like that, and it's really bugging me. Any ideas?