First off, we've never had a known security vulnerability. We check our very thoroughly, ensure that our SQL queries are secure, and practice best security behavior when coding to ensure nothing 'bad' is in our code. Of course, nothing is ever 100% guaranteed.
In the case that we had a security vulnerability, it would depend on what version the problem was found in and the severity of the issue. If it was in a release from the last 6 months (so some active users would still have it), we'd post in the forums or somewhere else the code required to implement the fix. Beyond 6 months, we'd need to take into consideration a lot of factors to determine how to publicize a fix, and if doing so is the right thing to do. As always, Facebook changes frequently, and the fix required may be to disable some functionality if the change was due to an issue on their end.
We value the security of our users very much, and will do what we can to make sure they aren't running an insecure version of JFBConnect, if it existed.
Hope that explains,
Alex