Show only some sections in TOC using beamer

Question

I am preparing a presentation in beamer. In addition to slides I will present, I want to include some extra slides for possible questions. For these extra slides, I would like to use sections and subsections, so I can navigate the complete document using bookmarks. However, I don't want these sections to appear in the TOC slide, but only on the bookmarks navigation pane of the pdf viewer. Any idea how I can do that?

For reference, I'm posting an image of how I would like the document to look like:

Answer 1

As an alternative to the \appendix command from leandriis answer you could place your extra slides in a separate \part:

\documentclass{beamer}

\begin{document}

\begin{frame}
\tableofcontents
\end{frame}

\section{main}
\begin{frame}
    abc
\end{frame} 

\section{more main}
\begin{frame}
    abc
\end{frame} 

\part{second part}
\section{backup}
\begin{frame}
    abc
\end{frame} 

\end{document}

Answer 2

Thanks for your solutions leandriss and samcarter. Both of them work like a charm!

I also found another solution using the package bookmark, in case one would like to hide selected sections (anywhere in the document) from the TOC. Here is the code:

\documentclass{beamer}
\usepackage{bookmark}

\begin{document}
\frame{\frametitle{Table of contents}
\tableofcontents
}

\section{Main Section 1}
\frame{Main Section 1}

\section{Main Section 2}
\frame{Main Section 2}

\section{Main Section 3}
\frame{Main Section 3}

\bookmark[page=5]{Questions Section 1}
\section*{Questions Section 1}
\frame{Questions Section 1}

\bookmark[page=6]{Questions Section 2}
\section*{Questions Section 2}
\frame{Questions Section 2}

\end{document}

Answer 3

You could make use of the \appendix command as shown in the following MWE:

\documentclass{beamer}
\begin{document}
\begin{frame}
\tableofcontents
\end{frame}
\section{First Section}
\begin{frame}
some text
\end{frame}
\appendix
\section{First Section in Appendix}
\begin{frame}
some additional text
\end{frame}
\end{document}

Sections in the appendix are hidden from the table of contents but are listed in the pdf bookmarks.