From the censor package documentation:
Additionally, as of version 2.0, there is provided a block-censor capability, for redacting larger blocks of text. This new command is \blackout, and is used in the form \blackout{Block of text}. This nice thing about this command is that it can stretch across line and paragraph boundaries conveniently.
However, the \blackout command will only black out the actual words of the text, while blank spaces and periods keep visible. To overcome this, a new command was introduced:
To this end, the \xblackout command is introduced in V3.10, which blacks
out the text more completely, while simultaneously preserving the
layout indentical to that of the uncensored document.
The following MWE and screenshot show the usage and respective output of the two commands in your example document.
\documentclass{article}
\usepackage{censor}
\begin{document}
Hello, world. \blackout{This is information I would like withheld from
public knowledge. It is extremely sensitive.}
Hello, world. \xblackout{This is information I would like withheld from
public knowledge. It is extremely sensitive.}
\end{document}
