\begin{frame}[fragile]
\frametitle{Be careful!}
PPTP (pppd or OS built-in)

Reasons:
\begin{itemize}
\item only a few configuration comply with the security requirements
\end{itemize}

Once again:

\url{http://www.heise.de/security/artikel/Der-Todesstoss-fuer-PPTP-1701365.html}
\end{frame}