Command on Ubuntu

Do you have a default desktop when you login to Ubuntu? If so the answer to you having nautilus is probably a positive unless you're using some other flavor of Ubuntu like Xubuntu, Kubuntu etc...

Now about virus... I highly doubt it, computer viruses don't affect Linux based OS' like Ubuntu, in any case you /should/ get a virus just deleting it would make it disappear forever 100%

Please take the time into reading this: http://linux.oneandoneis2.org/LNW.htm

This link may help.

http://freshtutorial.com/basic-ubuntu-command-tutorial-for-beginners/

This will tell your Ubuntu version (release).
https://help.ubuntu.com/community/CheckingYourUbuntuVersion

Very unlikely you will need to buy any programs.

What Larry said, about viruses is true. I have been using Ubuntu since 2008. No viruses. If it makes you more comfortable, you can use Clamav, it is located in Ubuntu Software Center.

if you press Ctrl+Alt+T you will geta terminal. Can you then run:

sudo lshw -C display; lsb_release -a; uname -a

What is output

Thanks