The economy may be improving but, in many fields, there is still a glut of talent. Since you can only hire one or a handful of the myriad professionals you interview, some of them are going to be sore when they don't receive a job offer. After all, most of us see ourselves as more capable than we might be. I am still somewhat stunned when I don't nail down an assignment I have been chasing.
Those turned down could retaliate, particularly in this era of social media when it's convenient, easy, and low-cost to bring one's grievance to the attention of the world.
One financial-information startup in Manhattan handles this possibility by having prospects sign a bulletproof NDA (Non-Disclosure Agreement) right in the lobby, before they even enter the operations part of the company. The agreement specifies that what the prospects see and hear while interviewing is confidential. Disclosure of any kind to any entity, including the media, is verboten.
Initially, I assumed that the organization was attempting to protect trade secrets. However, through sources who have contacts at that enterprise I found out that they had had troubles with professionals they had turned down. Some tipped off reporters about the oddball, verging on what they perceived as abusive, interview tactics. Others tweeted about the seeming ways in which they were made to think they had the position which they didn't. Others chronicled what they perceived as sweatshop conditions.
It takes just a little of your lawyer's time to put together a comprehensive NDA for the human-resources aspects of your organization. It could save your brand a major hit.