I've had the same issue with box.net a few weeks/months ago. I only signed up for their service and never really used it, and I used a one-off email address tha

I've had the same issue with box.net a few weeks/months ago. I only signed up for their service and never really used it, and I used a one-off email address that is randomly generated and used only for the service. I do this regularly now. With each service I subscribe to, I first of generate a unique random email address, so if I start to get spam, I can either block this address only, or at least know where it was leaked...