I am just curious to know what kind of security softwares are used by everyone here to prevent server hacks, DOS attacks and other problems.

If you own your own server, an absolute must is mod_security. I have seen more servers saved by this software than any other software on the market. For use with Red Hat Unix based servers, but we also use it on Freebsd with Cpanel. Works on all the Red Hat flavours and all control panels.

For DOS, you can use mod_evasive but it does break Front Page extensions.

Well we use several mod security and several other software ones. But also you should probably use hardware protection to if you are really worried.

A firewall such as the snapgear firewall card is great if you wish to pay the monthly fee of having one installed in your server. The resource level of the server would decrease since the box doesnt have to spend so much time in an application state. If you want to pay a monthly fee for such a card, by all means this is recommended over any software firewall.

http://configserver.com/ has a free firewall and login failure daemon, which is free, and serveral paid for security things.

I think that regardless of how much security software or hardware you have on a server, it is always a good idea to setup a rsync with snapshot routine on the server to stream backups of all your data to a remote location. Many companies go out of business within 5 years because of data loss and hardware failure.