How dangerous is taking a DNA test?

I have been wanting to take a DNA test for a while now since I am curious about my family history but I am concerned with what companies can do with it. I've heard that some companies could sell that data to other companies and may use your DNA as a means of rejecting you from things such as medical insurance. How true is this? Are there any companies which are trustworthy and creditted? And do the benefits outweigh the risks?