As Apple's share of the computer market grows, so too does the chance that Mac users will be targeted by all kinds of different hacker schemes, including those involving phishing, spyware or remote code execution. I wrote recently about a new Trojan program that attacks Macintosh computers (at http://blog.eogn.com/eastmans_online_genealogy/2010/10/new-trojan-program-attacks-macintosh-computers.html) and I suspect Mac users will see more malware (malevolent software) in the future. Security firm Sophos is now offering a free version of its business antivirus software to Mac users.
Sophos Anti-Virus Home Edition for Mac comes with no strings attached and reportedly will be updated for as long as there is a need for it. Best of all, the program is available free of charge.
Sophos Antivirus Home Edition for Mac also detects malware written for Windows that Mac users can spread via USB drives and email. The software is a noncommercial version of Sophos Anti-Virus 7.2 for Mac, targeted at home users and modified so it is easier to install and use.
I downloaded and installed the new anti-virus software on my iMac desktop system today. I'll do the same to the MacBook laptop within a day or two. The installation was easy, typical of most Mac software. I don't have any method of testing its performance against real viruses and Trojans, however.
The new Sophos software works on any Mac with an Intel or PowerPC processor and OS X 10.4 (Tiger), 10.5 (Leopard) or 10.6 (Snow Leopard). It requires 256 megabytes of memory plus 150 megabytes of available disk space. I believe the requirement of 256 megabytes of memory is above and beyond whatever other memory is being used for applications at any moment. If your Mac has one gigabyte of memory or less, I would expect this program will slow the Mac significantly. Any Mac system with more than one gigabyte of memory installed probably won't display any performance degradation. My 27-inch iMac with 8 gigabytes of memory did not seem to slow down at all.
You can download the free Sophos Antivirus Home Edition for Mac at http://www.sophos.com/products/free-tools/free-mac-anti-virus/