By default, all error pages of your Apache contains the version number of your server, which is a jackpot for hackers if you’re using an old version. Each version has some deficiencies that could be exploited by the hackers. If you don’t want hackers to exploit your server, then make sure to disable ServerSignature using .htaccess file.
Just drop the following code to .htaccess file of your root folder:
# Disable server signature ServerSignature Off