The whole (!) public folder of 1.3 GB data has been downloaded in the past 10 times at a single day. That's 13 GB on a single day. If you multiply that with 30.5 you get 396.5 GB for an average single month.

I guess it was a single user doing that. If someone knows how to combat this problem of massive multiple downloads from a single IP address, please let me know. I feel sorry to have renamed the share.