Hi Sissi,
I received a few notifications. First, I received e-mail notification that my application had been received. Second, I received a separate e-mail notification each time I was shortlisted for a position. (This e-mail notification told me I had to "log on to provide feedback".) Finally, I received e-mail notification that my application had "progressed" and that feedback had to be given within a week. From there, things moved really quickly. When I logged in, one of the positions I was previously shortlisted for said "application selected". I had to confirm my interest. Now, the automated system says, "security clearance in progress" and NATO officials have been in touch with me (no more use of the automated system).
Hope that helps and good luck.
PS - If anyone else here is awarded an internship in the future (which seems possible given people have been shortlisted), please contact me!