Avira Free Mac Security
Full user review
"Good free Mac antivirus with no advertisements"
Scans and updates automatically and it does not take up a lot of space on my Mac. It has the option of a quick scan or a full system scan, which is good because the full system scan takes longer. You can also schedule scans to occur automatically and choose if the auto scans will be full or quick. Also has a custom scan option. Also, there are no advertisements which is pretty cool for a free antivirus.
It hasn't found anything bad yet. But that might just mean that my Mac is clean. The Windows version has options to upgrade to paid antivirus options, but Mac does not. Upgrade options would be nice to have for Mac.