The problem: In late 2005 a Deloitte & Touche auditor left a CD-ROM on his airline seat. The disc contained the names, Social Security numbers, and investment details of more than 9,000 current and former employees of security vendor McAfee, a Deloitte client. Poor McAfee. If you can't trust a Big Four accounting firm, who can you trust?

The solution: Handing off data to a contractor will always be a leap of faith. Limit the information you share, review security policies before doing business, and make contractors agree in writing to indemnify you if they're responsible for a security breach.