The following is an actual user-submitted question:
Q: How do I know whether an online people-search service that I pay for will not put my information (that I have to give to process a search request) into their own database for others to find if someone wants to do a search on me?
A: People search services get all of their information from publicly available sources of information, such as court records, marketing research databases, and address directories. If you do a free search using one of the people search services we reviewed, chances are you'll find that you're already listed—most people are, though the depth and amount of information can vary from person to person, and service to service.
The only information collected during sign-up should be billing information, including a current address. We know that individuals we looked up had never used a background check service before, and we were able to find current and past addresses, as well as other information. Addresses are pretty easy to find for most individuals, unless you live truly off the grid.
So, the services are pretty safe (Intelius's privacy policy states how your information can be used, and the case you described is not part of their use policy). If you're curious, do a search on yourself, and see what comes up.