When you send people passwords and private links via email or chat, there are copies of that information stored in many places. If you use a one-time link instead, the information persists for a single viewing which means it can't be read by someone else later. This allows you to send sensitive information in a safe way knowing it's seen by one person only. Think of it like a self-destructing message, a One Time Secret.
If your web site is hosted by ADDR.com, you need to read this MSNBC report immediately. Passwords and credit card numbers appear to have been stolen.