Which free anti virus program to install on os x lion?

Question

Hi;
which anti virus program do you advise to install on mac os x lion?

Answer 1

Mac OS X versions 10.6.7 and later have built-in detection of known Mac malware in downloaded files. The recognition database is automatically updated once a day; however, you shouldn't rely on it, because the attackers are always at least a day ahead of the defenders. In most cases, there’s no benefit from any other automated protection against malware.
The most effective defense against malware is your own intelligence. All known Mac malware takes the form of trojans that can only operate if the victim is duped into running them. If you're smarter than the malware attacker thinks you are, you won't be duped. That means, primarily, that you never install software from an untrustworthy source. How do you know a source is untrustworthy?
Any website that prompts you to install software, such as a “codec” or “plug-in,” that comes from that same site, or an unknown site, is untrustworthy.
A web operator who tells you that you have a “virus,” or that anything else is wrong with your computer, or that you have won a prize in a contest you never entered, is trying to commit a crime with you as the victim.
“Cracked” versions of commercial software downloaded from a bittorrent are likely to be infected.
Software with a corporate brand, such as Adobe Flash, must be downloaded directly from the developer’s website. No intermediary is acceptable.
Follow these guidelines, and you’ll be as safe from malware as you can reasonably be.
Never install any commercial "anti-virus" products for the Mac, as they're all counter-productive. If you need to be able to detect Windows malware in your files, use ClamXav -- nothing else.