Anyone can go to http://uptime.netcraft.com/up/graph/ and enter your IP or domain name and get results back from your server such as:

Apache/1.3.29 (Unix) mod_auth_passthrough/1.8 mod_log_bytes/1.2 mod_bwlimited/1.2 PHP/4.3.4 FrontPage/5.0.2.2634 mod_ssl/2.8.16 OpenSSL/0.9.7a 

Giving this amount of details regarding your server can be a risk if your not up-to date with certain software. To disable this do the following:

login as root and from the command prompt enter:

pico /usr/local/apache/conf/httpd.conf

Then hold ctrl button and enter ServerSignature On

And change to:

ServerSignature Off

Also add this below it:

ServerTokens ProductOnly

Then ctrl + x and type Y to save your changes. Once your done restart apache and check your server with the above link.