Privatize is an interesting tool for Twitter users hiding links unless the person is specified in the tweet. What this means is that you tweet from Privatize specifying someones Twitter name and the link gives an error if they are not listed and verified via the Twitter oAuth. Here are the three simple steps:
If someone not authorized tries to open it they are presented with the following error screen:
Quite a simple application that opens up using Twitter to send almost a direct message without following each other. While no one can guarantee this is totally secure, it is better than sending public links or links everyone of your followers could open.
There is always file sharing, email and other ways. Check out Privatize here.