This is happening to me as well. Not only do they pop into my home sim, but they will periodicly land on my while I am out shopping or randomly traveling the grid. There is only one sim I have not seen them pop into. It's making me more than a little paraniod as I value my privacy. I am pretty sure they are bots, but thier purpose eludes me. I've taken to letting on certain Brenden know where I am heading before I get there to be helpful, as I see him most of all.