Originally Posted by Puzzle
1. Which anti-virus software is free and recommended?
Welcome to the forum
To expand a bit on what 273 has said, in most cases, an antivirus program is not needed for Linux as the vast majority of malware is written for Windows, not Linux or Mac. However, if you still find you need or desire one, you can use ClamAV, which should be available in the repositories using the Synaptic package manager. There is additional information here
which should be useful.
Information about other free AV's for Linux can be found here.
although some links in the latter are no longer functioning. I would also avoid Comodo at the moment as there seems to be an issue with missing dependencies at the moment.