2010 WordPress Theme – Updates

I read somewhere that the 2010 default theme is no longer being updated. First of all, is this true? If it is true, should I be concerned about security? I am not using this theme, but one of my clients is. Ultimately, I think that my client should move to a more responsive theme such as 2016. However, I would like to be able to tell him if the 2010 theme will make his site more vulnerable. Any information would be appreciated!