How to get api to do geocoding?

I have used Tele-Atlas/TomTom geocoding service which is now been discontinued. I'm trying to find an alternative that would return most or all of the same variables.

1. How do I get access to the API?

2. How is the security? My data is highly sensitive and I have to be 100% there will be no way the data can be viewed or saved.

3. I have to geocoding around 100,000 addresses. Will this be an issue?

Thank you