The DNN security has been improved from the first versions of the platform. Diverse controls, gratuitous or paid, have been created to help the users to improve the security by diverse techniques of which information can be found on the Internet.
Personally, it was interesting to me the use of an extra code that users must enter for validation to complete. This code is presented/displayed in form of an image with small distortions to avoid that automated programs enter or register a site.