The BSD varients (FreeBSD, NetBSD, OpenBSD, etc) are UNIX based operating systems that work on Intel PC based systems that have a reputation for being highly optimised, highly secure and excellent (when decently configured) for keeping hackers at bay.
Linux does not compare all that well to BSD: having a reputation of being a hacker's paradise to break into compared to BSD (FreeBSD at least). FreeBSD (and the other BSD's) run some of the most intensely hit servers on the globe, including ftp://ftp.cdrom.com. It can be said that the nicest thing you can do for a hacker is replace Windows with Linux as not only is it potentially easier to hack (one of the benefits of open source), but the system becomes worth hacking into. The same cannot necessarily be said with BSD based UNIX's which are built of sterner stuff to keep hackers at bay.
Thus the BSD based operating systems of which FreeBSD is one - have a reputation of being better designed (by gurus no less!), more secure (and more security conscious) and more robust than most other operating systems (including Linux - an operating system - it is claimed - "written by kiddies - for kiddies"). Refer to: FreeBSD, OpenBSD and SuSE 6.2 Eval Review by Keith Rankin: "The differences between FreeBSD and Linux used to be much more obvious than they are now. Now it comes down to theology. The BSD world is still the 'high church' or Druid Unix. Blood will be spilled on a stone altar at midnite when star systems are in a certain alignment to learn the ways of this tribe. Linux is a happier world. The spirits of Captain Kirk, Peter Pan and good beer come to mind." ("Buckets of Blood" and non-alcoholic prudery is official CCP14 computer operating system policy)