Answer by Rajesh Pantula for Do I need to have antivirus software installed?

Yes Ubuntu has a default firewall, but you need to configure it

Ubuntu uses ufw to configure the firewall. But it may not be enabled by default.

To enable the firewall open a terminal and type:

sudo ufw enable

Further info can be found in ufw's man page. In a terminal type:

man ufw

Coming to antivirus part, ubuntu does not have a default antivirus, nor does any linux distro I know, You dont need a antivirus program in linux. Although, there are few available for linux, but linux is pretty much safe when it comes to virus.