I wouldn't call it a security breach, but more a shared computer issue that may or may not be a problem for you & client. To clarify what I said earlier: My husband and I share my hard drive for files. If he opens, makes changes and saves a file, and I have the same file open and I'm making changes at the same time, the computer will save it as two separate files - one with his changes and one with mine.
In Dropbox, files are labeled "conflicted copy" with our username. It's nothing bad, just something to be aware of. In fact, for a spreadsheet our client put together and sharing with team (not just us), this issue caused us to move to Google Docs (Drive) and a Google website. This is all internal and settings can be made to keep everything private. Once you have one site setup, you can duplicate it too. Like most of Google's services, it's free! You might check that out, you can upload files, communicate, etc. I never found Basecamp to work well enough, maybe because our business is so specialized with one niche.
As far as not receiving updates from your thread when you "unsubscribe" (in the past that
has been the right button), a good place to look quickly to see if any responses have been posted: when you're signed in, at the bottom of the main forum list is a list of your most recent threads you've started. I know it's a hassle
