can't download

[iamfe]

Ok. My brother says his computer cuts off about halfway through downloading and the little box says not a valid app or publisher cant be verified. Can anyone tell me why this is happening or more importantly, how to fix it?

[rojash]

Is he on dial-up or broadband?

[ACtheTROLL]

downloading what?
and where to
is he using the save or open option?

[iamfe]

He is trying to download an instant messenger. aol or yahoo. I am pretty sure his internet is not dial-up and I don't know whether he clicks save or open. Which should he choose?