It works similar to herdscan's v-scan-procedure, which is scanning simultaneously through multiple proxies to the research lab's servers (kaspersky, norton, mcafee, glab, etc.) - when uploading you shouldn't even notice a drop of packets on your end. It's good though that this feature has been implemented into the Nexus. Imagine what could happen if someone would upload a potentially harmful file here and cloak it as modfile with proper descriptions - making it look like it would actually be a legit mod. Users/downloaders could infect their systems up to a hundredfold in 1h, given the usual traffic that's being produced daily.