Whenever you open up your unreleased software to the outside world, you are exposed to some risk. As with most things in Rainforest, it's worth weighing up the risk you're exposed to against the complexity of mitigating that risk.
Typically most of our customers are testing a Staging server minutes before that code is shipped to Production and open to the public. If this is your use case, there's not much that a tester can do that a regular user cannot do once the code is live. That said, there are several things to consider.
Terms of Service
The most basic protection is the Terms of Service that all testers are subject to. This differs depending on the crowd they come from, we currently use two main crowd providers, and all your testers are subject to one of these:
You must ensure that all data that your testers see and is personally identifying is sanitized correctly.
Good Staging and QA environments mirror Production environments as closely as possible. (If this sounds scary to you, our CTO's blog post on Optimal Environment Setup is well worth a read). Part of that is ensuring you have realistic data that is similar to what's on Production. Credit card numbers, personal email addresses, phone numbers should all be obscured. Since this is all in your database, we can't help you with the implementation of this, although we can help with best practices.
How much risk is there?
Most of our testers make their living on Rainforest. We have thousands of workers who rely on Rainforest to pay their bills and put food on the table for their family. They do not treat this relationship lightly, and they work hard and diligently to do their job well. They are not driven by short term motivations and since we have a single crowd of testers with many customers sharing one crowd, each tester will test and see multiple websites and apps each testing session. It's worth considering this when assessing the level of risk.
Our testers can sign a custom NDA for you! Find out more here.