The term "data seepage" has been coined to describe the information that your computer willingly broadcasts without you necessarily knowing about it or approving of it.

More on the subject here:

You can also download the BlackHat presentation slides and the Ferret 1.0 sniffing tool using links at the bottom.

OK, I know that sniffing tools are old hat and ten a penny, but this one takes the legwork out of assessing this particular issue.............. and I am inherently lazy