I can't. However, unless you built literally your entire system from source code and all of the programs that run on it and analysed that source code yourself p

I can't. However, unless you built literally your entire system from source code and all of the programs that run on it and analysed that source code yourself personally, you can't guarentee that about anything. It's a matter of degree of trust. This is what Spideroak's business is built on. Sure, I'd like it if their client would be open source, however in the mean time they're still a better option than Dropbox for security conscious people and they have been working for a while to make as much as possible open source. [0] [0] https://github.com/SpiderOak https://github.com/SpiderOak