To sum up, antivirus is mainly interesting if FreeBSD is acting as a fileserver and/or mailserver for a Windows based computer network. Even if Windows virus will not have any effect on BSD, if not detected the virus can be downloaded and can be distributed to windows computers when "Bill multiple Gates " access the server.
But, for a non corporate use this kind of protection is not quite necessary as Windows workstation can have his own antivirus solution. Today Comodo distributes for free his powerfull Comodo x64 native Workstation Internet Security Suite which is far better than Clamav.
But but... thinking further if we speak more generally about security, not dealing only with viruses and malwares....
Also there is very few malwares for BSD, having an heuristic protection is quite relevant because you can't ignore the case where a professional hacker like some Security Government Agencies create his own malware. As this code is not distributed so massively, the big problem is that you can ignore a very very long time his existence because there is an evidence, before a virus is declared "in the wild", security labs must first detect it...
One claims that there is no malware under BSD, but one will never be able to prove that and one can't claim that this will never be the case. The disadvantage of Windows is also... an advantage. Malwares are so massively distributed across the world that it facilitates his discovery by international security labs, for this reason having a good heuristic module under FreeBSD should be theoretically quite relevant.
Today Snort IDS solution can deal with some "security issues", but this solution is mainly based on rules. An heuristic protection offer an additional dynamic analysis against unknown threats (malware, rootkits...) by advising the user/administrator about suspicious activities.
Apart of the well known CLAMAV, today I know three commercial antivirus for FreeBSD, but I haven't tested any. For Linux there are more solutions. Almost every great security vendors have now a Linux solution, for BSD.... snif snif very few things.
- F-Prot : 3 versions, Workstation, Corporate file server, Corporate mail server
What is interesting is the fact that workstation version seems to have an heuristic real time module. I have never tried the product (today I simply use CLAMAV on my home made FreeBSD server, with Comodo Security Suite or Agnitum Security Suite on Windows workstations) so I can't give an opinion on the maturity of this heuristic module.
It seems that we can try the product 30 days. The price for the workstaion version seems to be the regular price for a common Windows license.
I don't speak about corporate versions as prices are generally not compatible with individual user budget.
http://www.f-prot.com/products/corporate_users/unix/
- Kaspersky : very very few info, it seems to be a corporate antivirus only (filer server and mail server) so likely too much expensive for a non corporate user, and I guess it does not offer a solid rock heuristic analysis as this product is targetting viruse analysis.
http://www.kaspersky.com/news?id=221
- AVG
Here is a link for a free Workstation version
http://free.avg.com/eu-en/129024
AVG seems to have a corporate FreeBSD build for FreeBSD email server
http://www.avgsecurity.co.za/component/avgproducts/?view=avgproducts&catid=84&Itemid=233
For all theses solutions, not much information about the FreeBSD platforms supported. For example KAV has long been only available for FreeBSD 9 ... i386. Same remark for AVG, you can see on the url link that source code for free workstation version is matching i386 platform only. For F-Prot they use the ambiguous terminology "x86" which would means "intel desktop platform including 32 and 64 bit) but you know there is a large misuse of this terminology as for a lot of people "x86" is faulty used as "32 bit"
The most reliable vendor for commercial FreeBSD AV solutions seems to be F-Prot. If it is working on "x86_64" one day I will probably make a try with Workstation version just to have a real idea.