Linux, unlike windows has typically not had the high profile (market share) nor has it been the target of widespread virus writing at this point. Many people think of linux as being immune to computer viruses and I suppose in some ways it is a completely different model for a virus writer to target. I think the main reason Linux (and Mac) hasn’t been targeted in the ways windows is that it is a better user/administrator privilege model from the outset (Windows is finally getting there and that helps.) I think the second reason is simply the minuscule market share (in comparison to Windows.) This may change and we may in the future see a need for linux antivirus or linux desktop antivirus.
The fact that there is not a dire need for linux antivirus hasn’t prevented some companies from providing a product that will run on linux. The primary purpose in some of these cases is not so that it can act as linux desktop antivirus, but so that a linux machine acting as a file server (or email gateway) for a network can scan and detect viruses in the files destined for windows users.
Clamav.net is THE open source antivirus solution. This can plug in to samba, can scan files as a standalone executable and can plug into mail software to scan inbound mail. (I’ve used this with amavisd for mail scanning.) They do frequent updates (several times per day as needed.)
Panda antivirus for linux – is available as a freeware non-supported version and it also operates from the command line. (Which means it should be possible to do scans of files shared to windows machines or integrate with something like amavis.)
Central Command has a linux version (I must admit I hadn’t heard of them before.)
Sophos also provides antivirus for linux.
Kaspersky also has a version of their antivirus available for the linux workstation.
Bitdefender brings their Antivirus Scanner for Unices to the table.
Antivir provids webgate and mailgate certified on linux.
Symantec has a linux antivirus scanner (although the date on the support page is 2005.)
McAfee provides their Virusscan enterprise for linux.
Trend Micro has Serverprotect for Linux as their linux antivirus solution.
So, although many people don’t yet see linux antivirus as a necessity there are certainly a lot of choices!