i am using ubuntu 16.04 do i need to install anti-virus in it?
If so please suggest the best one.

The short answer is no.

A more complicated answer goes like this. If you double boot Linux and Windows, suppose you download something that's actually a virus using Linux and then transfered it to Windows? Then Windows gets infected. In practice, you should have anti-virus in Windows. If you often pass things on to other people, you might want to check them first in Linux, and the answer is Clam
https://www.clamav.net/

But generally Linux is safe, as (1) the malware is normally written for Windows and (2) programs can't run in Linux until they've been labeled as programs in the filing system, and the malware can't label itself. Look at any file in /bin and check the permissions: you'll see a box labeled "allow execution as a program" has been ticked: until that is done, the program cannot run.

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http://ubuntu-manual.org/
https://help.ubuntu.com/lts/ubuntu-help/index.html
https://help.ubuntu.com/community/Antivirus

Should help you keep your investment.

Depends on the level of security you wish to have. The more best practices you learn and use, the more likely your data will be secure. As we have seen over the last few decades, no OS is secure.

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At home I use a Watchguard hardware firewall, a stateful-packet firewall with iptables (locked down as tight as I can get it, and rebuilt with cron every half hour), a separate Watchguard WAP, a pay vpn service, clamav, rkhunter, wireshark for periodic analysis, tripwire, unhide, honey pot, and reboot weekly. I am quite vigilant on top of everything else.

There is no such thing as set it and forget it with online security. You should read dmesg a few times so you can recognize out-of-place things. If you don't know what normal is, you'll never know when there's a problem.

During times of peace the wise man prepares for war.

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