The free AVG is one that dropped almost out of sight in reviews a few months ago, due to inadequate handling of a couple of "newer classes of malware," although it is again reported favorably in more recent reviews. It's not clear whether the return is because of release of a new version or just an update in existing ones. This fluctuation in ratings is characteristic of all but a few names in the business, (with reputable paid versions being much more "stable" than the free ones, although some lesser paid versions perform like yo-yos). There's nothing wrong with using free versions, but keeping them current may require a little closer management than for ones that automate it all.

On the other front:

Another OS X Trojan paves way for Mac zombie army

"The growing market penetration of Macs in the worldwide PC market, coupled with the general cluelessness of Mac owners ... has created a ripe field of millions of powerful, unprotected machines ready for exploitation by cyber criminals.

"And for a cyber criminal, the best kind of botnet to run would be one comprised of machines whose owners think they'll never be infected."

John