Unencrypted means that your data gets transmitted from your PC to their server with no protection whatsoever. Anybody who is smart enough to capture and record whatever you are transmitting, could put the pieces back together and see what was sent. Although this is unlikely, it sure is a risk.
In the best case scenario, only people who work for A-Drive would be able to see your data, although they probably have a policy that employees can't just look around other peoples data... but the possiblity exists.
A good company providing backup solutions usually have a backup of their data, which means more than one copy. It all really depends what type of system they have setup there.
My suggestions is to use this free backup for pictures, music, videos, documents that are non-sensitive. Also, you should have a local backup on your computer of everything on A-Drive... just in case.
A-Drive (http://www.adrive.com/) offers 50GB of free online storage, but the up and download in the "Basic" Storage Plan is unencrypted.
So how likely is it that somebody can see the stuff that I up and download? Do any copies of my data land on some servers during transmission and stay there?
Thanks for the answers!