Does BitTorrent Sync share my data?

Question

I have been interested in using BitTorrent Sync to synchronize my files. My question is: Is my encrypted torrent data being shared through 3rd party computers or only the computers I register? For example, if I install Sync on 3 machines, will all of that sync'd data only ever stay on those 3 machines and no data - encrypted or not - ever travels to other computers with Sync installed.

Answer 1

While Sync uses BitTorrent technology, it creates swarm only from your machines. Particularly in your case it will create a swarm from your 3 machines, that nobody could join, and will use p2p to effectively send data between them.

PS. I am involved in Sync development.

Answer 2

This is from bittorrent website:

The data is transferred in pieces from each of the syncing devices,
and BitTorrent Sync chooses the optimal algorithm to make sure you
have a maximum download and upload speed during the process.

EDIT: there is also a statement in unofficial faq:

Will me devices still sync when switched off?
BitTorrent Sync is not a cloud storage solution like
SkyDrive/DropBox/GDrive, etc - it doesn't sync your files to a "cloud",
therefore for one device to sync with another, both devices need to be online

First statement does not tell anything about communication with devices of other users. Last statement could hint, that there is no way to get to your data without having at least one of your own syncing machines turned on.