Rich Mogull has an important post at securosis.com for all folks interested in their privacy: If You Release It, You Can’t Control It:

"I’m consistently amused by the utter shock and dismay of various individuals and corporations when… gasp.. someone takes something they made public and does something… and you won’t believe this… unexpected and unapproved with it!"

Given that more than 150,000 people (by one estimate ) have access to the typical SSN, that certainly sounds public to me. So don’t be surprised when you become a victim.