For many sensitive web surveys, such as employee or patient surveys, there are two problems that online survey software alone can’t solve. http://apian.com/software/surveypro/web.php
Problem #1: people only open up when they know they’re completely anonymous
Problem #2: when they’re completely anonymous, you can’t keep them from stuffing the ballot box.
Cookies and logging IP addresses are both flawed. Cookies can be easily deleted, and both interfere with responses from people who share computers. This is unworkable with, say, factory floor or medical staff who use a shared computer. How to solve both problems at once for your online survey?
One way is to hire SurveyHost for third-party confidentiality. http://apian.com/services/surveyhost/ We can send out the emails for you, with individual passwords to prevent multiple submissions. You can tell your staff you don’t have access to the passwords, and sometimes this is sufficient for most respondents.
Or, you can go completely old school after you create your web survey with SurveyPro. Just mail merge the passwords onto postcards. Shuffle the postcards in front of your respondents and pass them out, one each. Everyone knows they’re not being tracked.