gistfile1.aux

\documentclass{article}
\usepackage{lipsum}

\makeatletter
\let\old@addcontentsline\addcontentsline
\def\trivial@addcontentsline#1#2#3{}
\def\hiddensection#1{%
  \let\addcontentsline\trivial@addcontentsline
  \section{#1}
  \let\addcontentsline\old@addcontentsline
}
\makeatother

\begin{document}

\tableofcontents

\section{A}
\lipsum[1]

\hiddensection{B}
\lipsum[2]

\section{C}
\lipsum[3]

\end{document}