I wouldn't trust anything to be private on the Internet.
Whatever it is someone, somewhere, will find a way to hack into it.
If the US military can have their systems broken into (as per the case a few weeks ago) what chance do you think you have with a forum?
I still use a motorcycle courier for transporting sensitive documents from my studio to wherever they need to go, even though it would be much more simple by email.
A legal case I was an expert witness in a few weeks ago had all the documents delivered and collected by courier even though ordinary messages were by email.
So, the answer to "are there measures that can be taken to reduce the risks?" is don't use the Internet if you want security.